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Magnetism and Magnetic Effects of Current PYQs – Physics, SSC & Railway

129 Magnetism and Magnetic Effects of Current (Physics) questions asked in recent SSC and Railway exams, newest first, with exam, date & shift, answers and solutions.

📚 129 questionsSSC 19 · Railway 110
12
SSC Stenographer 2026 – 12 September 2026 Shift 1 · Electromagnetic induction and Faraday's laws

Q1. What principle underlies the working of transformers, electric generators, and inductive charging systems?

  1. (a) Ohm's Law
  2. (b) Joule's Law
  3. (c) Faraday's Law of Electromagnetic Induction
  4. (d) Newton's Third Law
Answer & solution

Answer: (c) Faraday's Law of Electromagnetic Induction

Answer: Option 3 — Faraday's Law of Electromagnetic Induction
A transformer, a generator and a wireless charging pad all work the same way: a changing magnetic flux through a coil induces an EMF in it.
Ohm's law relates V, I and R, and Joule's law gives the heat produced — neither creates a current from a magnetic field.
Revision note — Electromagnetic induction
• Discovered by Michael Faraday in 1831: whenever the magnetic flux linked with a closed circuit changes, an induced EMF appears, equal to the rate of change of flux (EMF = −N × ΔΦ/Δt).
• Lenz's law supplies the minus sign — the induced current always opposes the change that produced it, a consequence of conservation of energy.
• A transformer works on mutual induction between a primary and a secondary coil, so it works only on AC, never on steady DC.
• An electric generator converts mechanical energy into electrical energy; the direction of the induced current is given by Fleming's right-hand rule.
• An AC generator collects current through slip rings; a DC generator uses a split-ring commutator.
• Inductive (wireless) charging uses mutual induction between a coil in the pad and a coil in the phone; an induction cooktop heats the vessel by eddy currents.
• SI unit of magnetic flux is the weber (Wb); of inductance the henry (H).
Do not mix these up
• Fleming's right-hand rule vs left-hand rule — the right hand is for the generator (induced current); the left hand is for the motor (force on a conductor).
• Faraday's laws of induction vs Faraday's laws of electrolysis — the same scientist, but the electrolysis laws deal with mass deposited at an electrode, not with induced EMF.
Also asked from this topic: the direction of an induced current by Lenz's law (opposes the change in flux); the EMF in a rod moving across a field (BLv); the collector of an AC generator (slip rings).
SSC Stenographer 2026 – 12 September 2026 Shift 2 · Earth's magnetism

Q2. Which of the following statements about the Van Allen Radiation Belts is incorrect?

  1. (a) The Van Allen belts are zones of charged particles trapped by Earth's magnetic field, predominantly composed of protons and electrons
  2. (b) The inner radiation belt lies closer to Earth and primarily contains high-energy protons, while the outer belt contains mostly electrons.
  3. (c) The radiation intensity of the Van Allen belts poses no operational hazard to satellites or human spaceflight missions passing through them.
  4. (d) Geomagnetic storms and solar activity can cause significant changes in the structure and intensity of the Van Allen belts.
Answer & solution

Answer: (c) The radiation intensity of the Van Allen belts poses no operational hazard to satellites or human spaceflight missions passing through them.

Answer: Option 3 — The radiation intensity of the Van Allen belts poses no operational hazard to satellites or human spaceflight missions passing through them.
The belts are a serious hazard: their energetic particles damage satellite electronics and solar cells and would give astronauts a dangerous dose.
Spacecraft are shielded or routed round them, the ISS orbits below them at about 400 km, and the Apollo crews crossed them as fast as possible.
The other three statements are correct descriptions of the belts.
Revision note — The Van Allen radiation belts
• Discovered in 1958 by James Van Allen from Geiger-counter data on Explorer 1, the first American satellite.
• Two main belts: the inner belt at about 1,000–6,000 km, rich in high-energy protons; the outer belt at about 13,000–60,000 km, dominated by electrons.
• The particles come from the solar wind and from cosmic-ray collisions in the atmosphere, trapped by the Earth's magnetic field (magnetosphere).
• The South Atlantic Anomaly, where the inner belt dips to a few hundred kilometres over South America, is where satellites suffer most upsets.
• NASA's Van Allen Probes (2012–2019) found a temporary third belt in 2013; geomagnetic storms swell and shrink the belts within hours.
• Polaris Dawn (September 2024), a private SpaceX crewed flight, deliberately flew through high-radiation zones to study the biological effects of space radiation.
Do not mix these up
• Van Allen belts vs ionosphere — the ionosphere (about 60–1,000 km) is a layer of the upper atmosphere that reflects radio waves; the belts lie far above it, in the magnetosphere.
• Van Allen belts vs auroras — auroras form when solar-wind particles guided by the field strike the upper atmosphere near the poles; the belts are the particles that stay trapped in space.
Also asked from this topic: the origin of the Van Allen belt particles (solar wind and cosmic rays, not the Sun alone); the cause of auroras near the poles (solar wind meeting Earth's magnetic field).
RRB Group D 2025-26 – 25 August 2026 Shift 1 · Force on a current-carrying conductor and Fleming's left-hand rule

Q3. A rectangular coil is placed in a uniform magnetic field. If the direction of the current is reversed, what is the effect on the force acting on each segment of the coil?

  1. (a) The magnitude of the force doubles
  2. (b) The force acts perpendicular to the plane of the coil
  3. (c) The magnitude of the force becomes zero
  4. (d) The direction of the force on each segment reverses
Answer & solution

Answer: (d) The direction of the force on each segment reverses

Correct Answer:
Correct Answer: Option 4 – The direction of the force on each segment reverses
Explanation:
The force on a current-carrying conductor in a magnetic field is given by F = IL × B (right-hand rule / left-hand rule for direction). If the direction of current (I) is reversed while the magnetic field (B) stays the same, the direction of the forcereverseson each arm of the coil (though its magnitude stays unchanged). This reversal of force direction is essential to the working principle of an electric motor's continued rotation via a split-ring commutator.
Important Facts:
• The magnitude of force F = BIL sinθ depends on current, field strength, and angle — not on current's direction.
• This principle underlies the working of an electric motor.
• Fleming's Left Hand Rule gives the direction of force on a current-carrying conductor in a magnetic field.
RRB Group D 2025-26 – 25 August 2026 Shift 2 · Magnetic field and field lines

Q4. Which property of magnetic field lines explains the absence of magnetic monopoles in classical electromagnetism?

  1. (a) They are always circular
  2. (b) They form continuous closed curves
  3. (c) They are denser near poles
  4. (d) They never intersect
Answer & solution

Answer: (b) They form continuous closed curves

Correct Answer:
Correct Answer: Option 2 – They form continuous closed curves
Explanation:
Magnetic field lines always formcontinuous closed loops— they emerge from the North pole, travel through the space outside the magnet, enter at the South pole, and continue inside the magnet back to the North pole, forming an unbroken loop. This property directly indicates that isolated magnetic poles (monopoles) do not exist in classical electromagnetism — every field line that leaves a 'north' region must eventually return to a 'south' region, unlike electric field lines which can start/end on isolated charges.
RRB Group D 2025-26 – 25 August 2026 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q5. How does the magnetic field produced by a current-carrying wire change with distance from the wire?

  1. (a) It decreases as distance increases
  2. (b) It increases as distance increases
  3. (c) It fluctuates randomly with distance
  4. (d) It remains constant at all distances
Answer & solution

Answer: (a) It decreases as distance increases

Correct Answer:
Correct Answer: Option 1 – It decreases as distance increases
Explanation:
The magnetic field produced by a current-carrying straight wire is strongest close to the wire anddecreases as the distance from the wire increases. For a long straight conductor, the magnetic field strength B is inversely proportional to the perpendicular distance r from the wire (B ∝ 1/r), as given by Ampere's circuital law / Biot–Savart law.
RRB Group D 2025-26 – 25 August 2026 Shift 3 · Electric generator and Fleming's right-hand rule

Q6. If the direction of the magnetic field is north to south and the conductor moves upward, using Fleming's Right Hand Rule, what is the direction of the induced current?

  1. (a) Towards East
  2. (b) Towards West
  3. (c) Towards the observer
  4. (d) Away from the observer
Answer & solution

Answer: (a) Towards East

Correct Answer:
Correct Answer: Option 1 – Towards East
Explanation:
By Fleming's Right Hand Rule: thumb = direction of motion, forefinger = direction of magnetic field, middle finger = direction of induced current. Here, motion is upward and the field points from north to south. Applying the rule (equivalent to the physical relation, current direction ∝ velocity × field), the induced current direction works out to be towards the East.
Important Facts:
• Fleming's Right Hand Rule is used for generators/induced current (motional EMF); the Left Hand Rule is used for motors/force on a current-carrying conductor.
• The three directions (motion, field, current) are always mutually perpendicular.
RRB Group D 2025-26 – 25 August 2026 Shift 3 · Force on a current-carrying conductor and Fleming's left-hand rule

Q7. A student uses Fleming's Left Hand Rule to determine the direction of force on a conductor. If the forefinger points north, and the middle finger points east, in which direction will the force act?

  1. (a) Upwards
  2. (b) Westwards
  3. (c) Downwards
  4. (d) Southwards
Answer & solution

Answer: (a) Upwards

Correct Answer:
Correct Answer: Option 1 – Upwards
Explanation:
By Fleming's Left Hand Rule: forefinger = direction of magnetic field, middle finger = direction of current, thumb = direction of force (motion) on the conductor. Here, the forefinger (field) points north and the middle finger (current) points east. Working out the mutually perpendicular directions, the thumb (force) points upward.
Important Facts:
• Fleming's Left Hand Rule applies to the motor effect — the force experienced by a current-carrying conductor in a magnetic field.
• The three directions (field, current, force) are always mutually perpendicular to one another.
RRB Group D 2025-26 – 21 August 2026 Shift 2 · Solenoid and electromagnet

Q8. Why does one end of a solenoid behave as a north pole and the other as a south pole?

  1. (a) The current creates a similar magnetic effect to a bar magnet
  2. (b) There is no current in the solenoid
  3. (c) The insulation creates the poles
  4. (d) The solenoid is naturally magnetic
Answer & solution

Answer: (a) The current creates a similar magnetic effect to a bar magnet

Correct Answer:
Correct Answer: Option 1 – The current creates a similar magnetic effect to a bar magnet
Explanation:
When current flows through a solenoid, the magnetic fields of its individual turns add up to produce a field pattern outside and inside the coil identical to that of a bar magnet, with one end behaving as a north pole and the other as a south pole (direction given by the right-hand thumb rule).
RRB Group D 2025-26 – 21 August 2026 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q9. A student observes that the compass needle deflection decreases as it moves farther from a current-carrying straight conductor. What is the most likely reason for this observation?

  1. (a) The electric current in the conductor decreases with distance
  2. (b) The shape of the wire affects field strength only at close distances
  3. (c) The magnetic field strength decreases as the distance from the conductor increases
  4. (d) The Earth's magnetic field becomes stronger with distance
Answer & solution

Answer: (c) The magnetic field strength decreases as the distance from the conductor increases

Correct Answer:
Correct Answer: Option 3 – The magnetic field strength decreases as the distance from the conductor increases
Explanation:
The magnetic field around a straight current-carrying conductor weakens with increasing distance from it (B is inversely proportional to distance, per the Biot-Savart/Oersted relation). As the compass moves farther away, the weaker field produces a smaller deflection of the needle.
RRB Group D 2025-26 – 21 August 2026 Shift 3 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q10. Which rule is used to determine the direction of the magnetic field at the centre of a circular current-carrying loop?

  1. (a) Right-hand thumb rule
  2. (b) Fleming’s left hand rule
  3. (c) Joule’s law of heating
  4. (d) Ohm’s law
Answer & solution

Answer: (a) Right-hand thumb rule

Correct Answer:
Correct Answer: Option 1 – Right-hand thumb rule
Explanation:
Theright-hand thumb rule(curl the fingers in the direction of current, thumb points in the direction of the magnetic field) is used to determine the direction of the magnetic field, including at the centre of a current-carrying circular loop.
Important Facts:
• Fleming's left-hand rule instead gives the direction of force on a current-carrying conductor in a magnetic field, not the field's direction itself.
RRB Group D 2025-26 – 21 August 2026 Shift 3 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q11. A technician wants to decrease the magnetic effect around a current-carrying wire without changing the wire's material or environment. Which method should be used?

  1. (a) Change the wire's path to a straight line
  2. (b) Reduce the amount of current flowing through the wire
  3. (c) Make the wire thinner without changing the current
  4. (d) Increase the length of the wire used
Answer & solution

Answer: (b) Reduce the amount of current flowing through the wire

Correct Answer:
Correct Answer: Option 2 – Reduce the amount of current flowing through the wire
Explanation:
The strength of the magnetic field around a current-carrying wire is directly proportional to the current (B ∝ I). Without altering the wire's material, thickness, or path, the only way to decrease the magnetic effect is toreduce the currentflowing through it.
Important Facts:
• Changing the wire's thickness or path would alter its physical configuration/environment, which the question rules out.
RRB Group D 2025-26 – 20 August 2026 Shift 2 · Domestic electric circuits, fuse and earthing

Q12. Why are all appliances in a domestic circuit connected in parallel?

  1. (a) To reduce the number of switches needed
  2. (b) To ensure each appliance gets equal potential difference
  3. (c) To prevent short-circuiting in wires
  4. (d) To save electricity in the household
Answer & solution

Answer: (b) To ensure each appliance gets equal potential difference

Correct Answer:
Correct Answer: Option 2 – To ensure each appliance gets equal potential difference
Explanation:
In a domestic parallel circuit, every appliance is connected directly across the same two points of the supply line, so each receives the same (full mains) potential difference regardless of the others, allowing each appliance to operate at its rated voltage and to be switched on/off independently.
Important Facts:
• In a series circuit, voltage divides among components and all components stop working if one fails — unsuitable for households.
• Parallel wiring does not itself prevent short-circuiting; fuses/circuit breakers are used for that.
RRB Group D 2025-26 – 20 August 2026 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q13. A student wants to design a device where the magnetic field due to a straight conductor is maximized at a certain point. Which modification will be most effective in increasing the field strength at that point?

  1. (a) Place the conductor horizontally
  2. (b) Increase the thickness of the wire
  3. (c) Increase the current through the conductor
  4. (d) Use a non-magnetic wire material
Answer & solution

Answer: (c) Increase the current through the conductor

Correct Answer:
Correct Answer: Option 3 – Increase the current through the conductor
Explanation:
The magnetic field strength (B) produced by a straight current-carrying conductor is directly proportional to the current flowing through it (B ∝ I). Increasing the current is the most direct and effective way to increase the field strength at a given point.
Important Facts:
• The orientation of the conductor or its thickness does not increase field strength the way current does; the wire material only matters if it affects resistance/current-carrying capacity.
RRB Group D 2025-26 – 20 August 2026 Shift 3 · Domestic electric circuits, fuse and earthing

Q14. A family wants to minimize the risk of electrical fires in their home. Which of the following practices involving electricity is/are most effective in achieving this goal?

  1. (a) Relying on extension cords for all appliances in the home.
  2. (b) Using only low-power electrical appliances in all rooms.
  3. (c) Increasing the number of power outlets in each room.
  4. (d) Using circuit breakers and regularly checking wiring for faults.
Answer & solution

Answer: (d) Using circuit breakers and regularly checking wiring for faults.

Correct Answer:
Option 4 – Using circuit breakers and regularly checking wiring for faults.
Explanation:
Circuit breakers automatically cut off power during a short circuit or overload, and regularly inspecting wiring helps detect faults before they cause fires — this is the most effective fire-prevention practice among the options. Overloading extension cords or outlets, in contrast, increases fire risk.
RRB Group D 2025-26 – 19 August 2026 Shift 2 · Solenoid and electromagnet

Q15. A student wants to create a bar magnet using a current-carrying solenoid. Which arrangement of magnetic field lines would indicate that the solenoid is behaving like a bar magnet?

  1. (a) The field lines emerge from one end and enter the other end, forming closed loops outside the solenoid.
  2. (b) Inside the solenoid, the field lines are arranged along randomly curved paths.
  3. (c) The field lines rotate in a spiral pattern from one end of the solenoid to the other.
  4. (d) The field lines form straight and parallel lines only outside the solenoid.
Answer & solution

Answer: (a) The field lines emerge from one end and enter the other end, forming closed loops outside the solenoid.

Correct Answer:
Correct Answer: Option 1 – The field lines emerge from one end and enter the other end, forming closed loops outside the solenoid.
Explanation:
A current-carrying solenoid produces a magnetic field pattern very similar to that of a bar magnet: field lines emerge from one end (behaving like the North pole), travel through the space outside, and enter the other end (behaving like the South pole), forming continuousclosed loops. Inside the solenoid, the field lines are straight and parallel, indicating a uniform field — just like inside a bar magnet.
Important Facts:
• One end of a current-carrying solenoid acts as a north pole and the other as a south pole, determined by the direction of current flow (right-hand thumb rule).
• Uniform field lines inside a solenoid are used in devices like electromagnets.
RRB Group D 2025-26 – 19 August 2026 Shift 3 · Force on a current-carrying conductor and Fleming's left-hand rule

Q16. An electron enters a uniform magnetic field at right angles to it. If the magnetic field is directed into the page and the electron enters toward the right, what is the direction of the force acting on the electron?

  1. (a) upward
  2. (b) out of the page
  3. (c) into the page
  4. (d) downward
Answer & solution

Answer: (d) downward

Correct Answer:
Option 4 – downward
Explanation:
Using F = qv × B: the electron moves to the right and the field points into the page. For apositivecharge moving right with B into the page, v × B points upward (by the right-hand rule). Since the electron carries anegativecharge, the actual force is opposite to this, i.e., directeddownward.
Important Facts:
• The magnetic force on a charged particle is always perpendicular to both velocity and magnetic field.
• For a negative charge, the force direction is reversed compared to a positive charge under identical v and B.
Correct Answer: Option 4 – downward
RRB Group D 2025-26 – 18 August 2026 Shift 1 · Electric generator and Fleming's right-hand rule

Q17. In a generator, what would be the result if the coil is rotated at double the original speed in the same magnetic field?

  1. (a) The resistance of the coil will halve
  2. (b) The induced potential difference will be twice as large
  3. (c) The direction of current will reverse
  4. (d) The magnetic field strength will double
Answer & solution

Answer: (b) The induced potential difference will be twice as large

Effect of rotation speed on induced EMF
In an AC generator, the induced EMF (potential difference) is proportional to the rate of change of magnetic flux, which depends on the speed of rotation of the coil: EMF ∝ Angular speed (for fixed field and coil area).
Doubling the rotational speed doubles the rate at which the coil cuts magnetic field lines, so the induced potential difference becomes twice as large.
Correct Answer: The induced potential difference will be twice as large
RRB Group D 2025-26 – 18 August 2026 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q18. During an experiment, a student applies the Right Hand Thumb Rule to a vertical wire with current flowing upward. What is the direction of the magnetic field at a point directly east of the wire?

  1. (a) The magnetic field points towards the south at that point
  2. (b) The magnetic field points towards the west at that point
  3. (c) The magnetic field points towards the east at that point
  4. (d) The magnetic field points towards the north at that point
Answer & solution

Answer: (d) The magnetic field points towards the north at that point

Right Hand Thumb Rule
Point the right thumb in the direction of current flow (upward, along the wire). The curled fingers show the direction of the magnetic field lines circling the wire.
Taking up as the current direction, and setting East as +x and North as +y: the magnetic field direction at a point is given by (current direction) × (radial direction to the point). At a point due East of the wire, this cross product pointsNorth.
(Physically: viewed from above looking down along the current, the field circulates counter-clockwise; at the East side of the wire this circulation direction is Northward.)
Correct Answer: The magnetic field points towards the north at that point
RRB Group D 2025-26 – 18 August 2026 Shift 2 · Solenoid and electromagnet

Q19. Why are field lines inside a solenoid described as parallel straight lines?

  1. (a) Because the magnetic field is the same at all points inside, indicating uniformity
  2. (b) Because the solenoid is very short in length
  3. (c) Because parallel lines suggest the field varies greatly
  4. (d) Because the current changes direction rapidly
Answer & solution

Answer: (a) Because the magnetic field is the same at all points inside, indicating uniformity

Magnetic Field Inside a Solenoid
Inside a current-carrying solenoid, the magnetic field lines are parallel to the axis and equally spaced, indicating that the magnetic field has thesame magnitude and direction at every point inside— i.e., it is uniform.
Correct Answer: Because the magnetic field is the same at all points inside, indicating uniformity
RRB Group D 2025-26 – 17 August 2026 Shift 1 · Force on a current-carrying conductor and Fleming's left-hand rule

Q20. In Fleming's Left Hand Rule, which finger represents the direction of the magnetic field?

  1. (a) The ring finger
  2. (b) The thumb
  3. (c) The index finger
  4. (d) The middle finger
Answer & solution

Answer: (c) The index finger

Fleming's Left Hand Rule
In Fleming's Left Hand Rule, the thumb, the index (fore) finger, and the middle finger are stretched mutually perpendicular to each other, representing:
• Thumb → direction of Motion/Force on the conductor
• Index (fore) finger → direction of the Magnetic Field
• Middle finger → direction of Current
A common mnemonic: 'FBI' (Force–thumb, Field–first finger, Current–middle finger).
Correct Answer: The index finger
RRB Group D 2025-26 – 17 August 2026 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q21. An experiment uses a compass near a straight current-carrying wire. What does the compass needle indicate?

  1. (a) The compass needle points radially away from the wire
  2. (b) The compass needle aligns parallel to the wire
  3. (c) The compass needle shows no movement
  4. (d) The compass needle aligns tangentially to the magnetic field circle around the wire
Answer & solution

Answer: (d) The compass needle aligns tangentially to the magnetic field circle around the wire

Magnetic Field Around a Straight Current-Carrying Wire
The magnetic field lines around a straight current-carrying wire are concentric circles centred on the wire (right-hand thumb rule). A compass needle placed near the wire aligns itself along the direction of the magnetic field at that point, i.e., italigns tangentially to the circular magnetic field linesaround the wire.
• The needle does not point radially away from the wire, nor parallel to the wire itself.
• The needle does show deflection/movement in presence of current, ruling out 'no movement'.
Correct Answer: The compass needle aligns tangentially to the magnetic field circle around the wire
RRB Group D 2025-26 – 14 August 2026 Shift 1 · Force on a current-carrying conductor and Fleming's left-hand rule

Q22. A technician reverses the direction of current in a conductor placed in a magnetic field. According to Fleming's Left Hand Rule, what will happen to the direction of force on the conductor?

  1. (a) The force direction will remain unchanged
  2. (b) The force direction will reverse
  3. (c) The force will always increase
  4. (d) The force will disappear
Answer & solution

Answer: (b) The force direction will reverse

Answer: Option 2 – The force direction will reverse.
• By Fleming's left-hand rule, reversing the currentreverses the forcedirection.
RRB Group D 2025-26 – 14 August 2026 Shift 2 · Domestic electric circuits, fuse and earthing

Q23. Suppose all the 5 A sockets in a house are replaced with 15 A sockets and several high-power electrical appliances are connected to each. What kind of potential risk could this create and why?

  1. (a) It ensures that all appliances operate at low voltage.
  2. (b) It increases the risk of overloading and a possible short-circuit due to excessive current flow.
  3. (c) It stops the fuse from working in any situation.
  4. (d) It reduces the risk of electrical accidents in the house.
Answer & solution

Answer: (b) It increases the risk of overloading and a possible short-circuit due to excessive current flow.

Answer: Option 2 – It increases the risk of overloading and a possible short-circuit.
• Replacing 5 A sockets with 15 A sockets and adding many high-power appliances lets much larger currents flow,overloading the wiring and risking a short circuit/fire.
RRB Group D 2025-26 – 14 August 2026 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q24. A student places a compass near a straight, current-carrying conductor and observes the needle deflect. What does this observation indicate about the region around the conductor?

  1. (a) The region becomes gravitationally active
  2. (b) Heat is produced around the conductor
  3. (c) There is a magnetic field present around the conductor
  4. (d) An electric field is generated around the conductor
Answer & solution

Answer: (c) There is a magnetic field present around the conductor

Answer: Option 3 – There is a magnetic field present around the conductor.
• A deflected compass needle shows amagnetic fieldaround the current-carrying conductor (Oersted's observation).
RRB Group D 2025-26 – 13 August 2026 Shift 3 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q25. Why are magnetic field lines due to current in a straight conductor denser near the wire and farther apart as distance increases?

  1. (a) Because the magnetic field becomes uniform farther away
  2. (b) Because the current in the wire decreases with distance
  3. (c) Because of interference from external magnets only
  4. (d) Because magnetic field strength decreases with increasing distance from the wire
Answer & solution

Answer: (d) Because magnetic field strength decreases with increasing distance from the wire

Answer: Option 4 – Because magnetic field strength decreases with increasing distance from the wire.
• Field B ∝ 1/r, so lines aredenser near the wireand spread out farther away.
RRB Group D 2025-26 – 13 August 2026 Shift 3 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q26. A student wants to use the Right Hand Thumb Rule to determine the direction of the magnetic field around a current-carrying straight conductor. Which of the following steps is essential in applying the rule correctly?

  1. (a) Point the thumb in the direction of current
  2. (b) Use the left hand for orientation
  3. (c) Wrap fingers in the direction of the conductor
  4. (d) Align the thumb with the magnetic field
Answer & solution

Answer: (a) Point the thumb in the direction of current

Answer: Option 1 – Point the thumb in the direction of current.
• In the right-hand thumb rule, thethumb points along the currentand the curled fingers show the field direction.
RRB Group D 2025-26 – 12 August 2026 Shift 1 · Electromagnetic induction and Faraday's laws

Q27. A coil of wire is moved rapidly into a region with a strong magnetic field. Which change will most likely increase the magnitude of the induced current in the coil?

  1. (a) Rotating the coil at the same speed within the field
  2. (b) Increasing the speed at which the coil enters the magnetic field
  3. (c) Holding the coil stationary in the field
  4. (d) Using a thicker wire for the coil
Answer & solution

Answer: (b) Increasing the speed at which the coil enters the magnetic field

Answer: Option 2 – Increasing the speed at which the coil enters the field.
• Faster change of flux induces a larger EMF/current (Faraday's law).
RRB Group D 2025-26 – 12 August 2026 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q28. A student wants to increase the magnetic field strength around a straight conductor carrying current. Which combination of changes will most effectively achieve this?

  1. (a) Keeping the current constant and changing the observation point to any location.
  2. (b) Decreasing the current and moving the observation point farther from the conductor.
  3. (c) Increasing the current and bringing the observation point closer to the conductor.
  4. (d) Increasing the current while moving the observation point farther away.
Answer & solution

Answer: (c) Increasing the current and bringing the observation point closer to the conductor.

Answer: Option 3 – Increasing the current and bringing the observation point closer.
• Magnetic field B ∝ I and ∝ 1/r, somore current + smaller distancegives the strongest field.
RRB Group D 2025-26 – 12 August 2026 Shift 3 · Solenoid and electromagnet

Q29. Why can a solenoid be used to magnetise a piece of soft iron placed inside it?

  1. (a) Because the solenoid produces a strong and uniform magnetic field inside it
  2. (b) Because the solenoid creates a weak and scattered magnetic field inside it
  3. (c) Because the solenoid blocks magnetic fields from entering soft iron
  4. (d) Because the solenoid produces a non-uniform field only outside it
Answer & solution

Answer: (a) Because the solenoid produces a strong and uniform magnetic field inside it

Answer: Option 1 – Because the solenoid produces a strong and uniform magnetic field inside it.
• A current-carrying solenoid has astrong, uniform magnetic fieldinside (like a bar magnet), which magnetises the soft-iron core.
RRB Group D 2025-26 – 11 August 2026 Shift 1 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q30. The right hand thumb rule is also known as _______________.

  1. (a) Ohm's rule
  2. (b) Fleming's rule
  3. (c) Maxwell's corkscrew rule
  4. (d) Faraday's rule
Answer & solution

Answer: (c) Maxwell's corkscrew rule

Answer: Option 3 – Maxwell's corkscrew rule.
• The right-hand thumb rule (direction of magnetic field around a current) is also calledMaxwell's corkscrew rule.
RRB Group D 2025-26 – 11 August 2026 Shift 2 · Electromagnetic induction and Faraday's laws

Q31. Which setup is most likely to produce a larger induced current in a coil?

  1. (a) Using fewer turns of wire in the coil
  2. (b) Using more turns of wire in the coil
  3. (c) Using a smaller magnet
  4. (d) Moving the magnet more slowly
Answer & solution

Answer: (b) Using more turns of wire in the coil

Answer: Option 2 – Using more turns of wire in the coil.
• Induced EMF/current increases with thenumber of turns(and with faster motion and a stronger magnet).
RRB Group D 2025-26 – 11 August 2026 Shift 3 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q32. If the direction of current in a straight conductor is reversed, what will be the effect on the direction of the surrounding magnetic field lines?

  1. (a) The magnetic field lines will become weaker
  2. (b) The magnetic field lines will reverse direction
  3. (c) The magnetic field lines will remain unchanged
  4. (d) The magnetic field lines will become stronger
Answer & solution

Answer: (b) The magnetic field lines will reverse direction

Answer: Option 2 – The magnetic field lines will reverse direction.
• Reversing the currentreversesthe direction of the surrounding magnetic field (right-hand rule).
RRB Group D 2025-26 – 10 August 2026 Shift 3 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q33. What happens to the magnetic field around a straight current-carrying conductor if the direction of the current is reversed?

  1. (a) The magnetic field direction reverses around the conductor.
  2. (b) The magnetic field around the conductor becomes zero.
  3. (c) The magnetic field around the conductor disappears.
  4. (d) The magnetic field strength doubles around the conductor.
Answer & solution

Answer: (a) The magnetic field direction reverses around the conductor.

Answer: Option 1 – The magnetic field direction reverses.
• By the right-hand rule, reversing the currentreverses the directionof the circular magnetic field around the conductor (magnitude unchanged).
RRB Group D 2025-26 – 10 August 2026 Shift 3 · Electromagnetic induction and Faraday's laws

Q34. Two identical coils are placed near each other. If the current in the first coil is switched off suddenly, what will happen in the second coil?

  1. (a) A current is induced in the second coil that helps decrease the original magnetic field.
  2. (b) A current is momentarily induced in the second coil in a direction that tries to keep the magnetic field constant.
  3. (c) No current is induced in the second coil because the coils are not connected.
  4. (d) A steady current is induced in the second coil as long as the first coil remains off.
Answer & solution

Answer: (b) A current is momentarily induced in the second coil in a direction that tries to keep the magnetic field constant.

Answer: Option 2 – A current is momentarily induced that tries to keep the magnetic field constant.
• ByLenz's law, switching off the first coil's current induces amomentarycurrent in the second coil opposing the change – i.e. trying to maintain the field.
RRB Group D 2025-26 – 9 August 2026 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q35. Which statement best describes the application of the Right Hand Thumb Rule to a straight current-carrying conductor?

  1. (a) Thumb points in current direction, fingers curl in magnetic field direction
  2. (b) Thumb points in magnetic field direction, fingers curl in current direction
  3. (c) Fingers point in current direction, thumb curls in magnetic field direction
  4. (d) Left hand is used for current, right for magnetic field
Answer & solution

Answer: (a) Thumb points in current direction, fingers curl in magnetic field direction

Answer: Option 1 — Thumb points in current direction, fingers curl in magnetic field direction
Right-Hand Thumb Rule: thumb = current, curled fingers = magnetic field → Option 1.
RRB Group D 2025-26 – 6 August 2026 Shift 2 · Domestic electric circuits, fuse and earthing

Q36. Electric fuses are used in household circuits primarily to ___________.

  1. (a) Interrupt the circuit if excessive current flows
  2. (b) Reduce voltage in the circuit
  3. (c) Store electrical energy for later use
  4. (d) Supply extra electricity when needed
Answer & solution

Answer: (a) Interrupt the circuit if excessive current flows

Answer: Option 1 — Interrupt the circuit if excessive current flows
A fuse melts andbreaks the circuitwhen current is excessive → Option 1.
RRB Group D 2025-26 – 5 August 2026 Shift 1 · Force on a current-carrying conductor and Fleming's left-hand rule

Q37. If the current in a conductor is doubled while it remains perpendicular to the same magnetic field, how does the force on the conductor change?

  1. (a) The force remains unchanged
  2. (b) The force doubles
  3. (c) The force reduces four times
  4. (d) The force is halved
Answer & solution

Answer: (b) The force doubles

Answer: Option 2 — The force doubles
Force on a current-carrying conductor F = BIL. Doubling I (B, L constant)doubles the force→ Option 2.
RRB Group D 2025-26 – 5 August 2026 Shift 2 · Electromagnetic induction and Faraday's laws

Q38. Which arrangement will result in the greatest induced current in a wire loop?

  1. (a) Keeping the loop stationary in a magnetic field
  2. (b) Moving the loop parallel to the field lines
  3. (c) Moving the loop slowly into a weak magnetic field
  4. (d) Moving the loop quickly into a strong magnetic field
Answer & solution

Answer: (d) Moving the loop quickly into a strong magnetic field

Answer: Option 4 — Moving the loop quickly into a strong magnetic field
Induced current increases with therate of change of flux; a fast motion into astrongfield gives the greatest induced current → Option 4.
RRB Group D 2025-26 – 5 August 2026 Shift 2 · Electric generator and Fleming's right-hand rule

Q39. In an experiment, a metal rod moves northward across a horizontal magnetic field directed east. According to Fleming's Right Hand Rule, what is the direction of the induced current in the rod?

  1. (a) The induced current flows eastward
  2. (b) The induced current flows vertically downward
  3. (c) The induced current flows westward
  4. (d) The induced current flows vertically upward
Answer & solution

Answer: (b) The induced current flows vertically downward

Answer: Option 2 — Vertically downward
By Fleming's Right-Hand Rule (motion north, field east), the induced current is directedvertically downward→ Option 2.
RRB Group D 2025-26 – 4 August 2026 Shift 1 · Electromagnetic induction and Faraday's laws

Q40. What happens when a conductor moves through a magnetic field?

  1. (a) The strength of the magnetic field increases.
  2. (b) The conductor heats up.
  3. (c) A potential difference is induced across its ends.
  4. (d) Light is produced in the conductor.
Answer & solution

Answer: (c) A potential difference is induced across its ends.

Answer: Option 3 — A potential difference is induced across its ends
Moving a conductor through a magnetic field induces anEMF (potential difference)— electromagnetic induction (Faraday's law) → Option 3.
RRB Group D 2025-26 – 4 August 2026 Shift 1 · Electric motor

Q41. A device uses the principle of magnetic fields around a current-carrying conductor to convert electrical energy to mechanical energy. Which device operates on this principle?

  1. (a) Galvanometer
  2. (b) Electric motor
  3. (c) Solar cell
  4. (d) Transformer
Answer & solution

Answer: (b) Electric motor

Answer: Option 2 — Electric motor
Anelectric motorconverts electrical energy into mechanical energy using the force on a current-carrying conductor in a magnetic field → Option 2.
RRB Group D 2025-26 – 4 August 2026 Shift 3 · Domestic electric circuits, fuse and earthing

Q42. What is the function of the cartridge (such as porcelain) encasing the fuse wire?

  1. (a) To increase the current flow through the fuse
  2. (b) To safely contain the melted fuse wire and prevent hazards
  3. (c) To act as a heat sink for the fuse
  4. (d) To improve the fuse's electrical conduction
Answer & solution

Answer: (b) To safely contain the melted fuse wire and prevent hazards

Answer: Option 2 — To safely contain the melted fuse wire and prevent hazards
The porcelain cartridgesafely encloses the melting fuse wire, preventing sparks/fire → Option 2.
RRB Group D 2025-26 – 3 August 2026 Shift 2 · Magnetic field and field lines

Q43. What does a higher degree of closeness of magnetic field lines indicate?

  1. (a) Stronger magnetic field at that region
  2. (b) Presence of electric field
  3. (c) Weaker magnetic field at that region
  4. (d) The field lines are about to cross
Answer & solution

Answer: (a) Stronger magnetic field at that region

Answer: Option 1 — Stronger magnetic field at that region
Thecloserthe magnetic field lines, thestrongerthe field. Widely spaced lines mean a weaker field → Option 1.
SSC GD 2026 – 18 May 2026 Shift 2 · Solenoid and electromagnet

Q44. What is the shape of the magnetic field lines around a current-carrying solenoid?

  1. (a) Random and irregular.
  2. (b) Parallel straight lines inside the solenoid and concentric circles outside.
  3. (c) Concentric circles centered on the solenoid.
  4. (d) Radial lines extending outward from the solenoid.
Answer & solution

Answer: (b) Parallel straight lines inside the solenoid and concentric circles outside.

Correct Answer: Parallel straight lines inside the solenoid and concentric circles outside — Option (b)
A solenoid is a cylindrical coil of wire through which current flows. The magnetic field of a current-carrying solenoid has the following characteristics: Inside the solenoid — the magnetic field lines are parallel, straight, and uniform (equidistant), indicating a strong, uniform magnetic field similar to that inside a bar magnet. The field inside is strong and nearly uniform. Outside the solenoid — the magnetic field lines emerge from one end, loop around the outside, and re-enter from the other end, forming closed loops similar to those of a bar magnet (which is what a solenoid essentially acts as). These external field lines spread out and are not uniform. One end of the solenoid behaves like a North pole and the other like a South pole.
Option (a) Random and irregular — Incorrect: The magnetic field of a solenoid is highly organised — uniform and parallel inside, and loop-shaped outside. It is definitely not random or irregular.
Option (c) Concentric circles centered on the solenoid — Incorrect: Concentric circles describe the magnetic field around a long, straight current-carrying wire (not a solenoid). A solenoid's field is parallel inside and bar-magnet-like outside.
Option (d) Radial lines extending outward from the solenoid — Incorrect: Radial lines are not characteristic of a solenoid's magnetic field; radial lines describe the electric field of a point charge or the field pattern between poles of a cyclotron magnet.
SSC GD 2026 – 9 May 2026 Shift 1 · Domestic electric circuits, fuse and earthing

Q45. On a home meter-board, which current rating (amp rating) is used for high power-rated appliances like geysers, air coolers, etc.?

  1. (a) 4A
  2. (b) 8A
  3. (c) 11A
  4. (d) 15A
Answer & solution

Answer: (d) 15A

Correct Answer: 15A — Option (d)
In Indian household electrical wiring, appliances are categorized by their power consumption and current requirements. High power-rated appliances such as geysers (water heaters), air conditioners, washing machines, refrigerators, and air coolers require a higher current and are connected to 15A (ampere) rated sockets, plugs, and circuit breakers/MCBs (Miniature Circuit Breakers) on the meter board. Low power appliances (fans, lights, televisions, mobile chargers) use 5A rated circuits. The Indian Standard IS 1293 specifies 5A and 15A as the two standard current ratings for domestic plugs and sockets, with 15A being the higher-capacity rating for heavy-duty/high-power appliances.
Option (a) 4A — Incorrect: 4A is not a standard current rating used in Indian household circuits; the standard ratings are 5A (low power) and 15A (high power).
Option (b) 8A — Incorrect: 8A is not a standard rating in Indian domestic circuits for this purpose; high-power appliances use 15A rated connections.
Option (c) 11A — Incorrect: 11A is not a standard current rating in Indian household electrical systems; the correct higher current rating for heavy appliances is 15A.
SSC GD 2026 – 9 May 2026 Shift 3 · Solenoid and electromagnet

Q46. What does the electromagnet do after being activated in an electric bell?

  1. (a) Attracts the iron strip towards itself
  2. (b) Pulls the contact screw
  3. (c) Switches off the bell
  4. (d) Melts the coil
Answer & solution

Answer: (a) Attracts the iron strip towards itself

Correct Answer: Attracts the iron strip towards itself — Option (a)
In an electric bell, when the circuit is closed (switch pressed): The current flows through the coil of wire wound around an iron core, creating an electromagnet. The activated electromagnet attracts the iron strip (armature) towards itself. This pulls the hammer (attached to the iron strip) to strike the bell/gong, producing the ringing sound. As the iron strip moves towards the electromagnet, it breaks the contact at the spring contact point, breaking the circuit. Without current, the electromagnet deactivates, releasing the iron strip. The spring restores the iron strip to its original position, re-completing the circuit. This cycle repeats rapidly, producing continuous ringing.
Option (b) Pulls the contact screw — Incorrect: The electromagnet attracts the iron strip (armature), not the contact screw. The contact screw is the fixed point; the iron strip moves towards the electromagnet.
Option (c) Switches off the bell — Incorrect: The electromagnet activating attracts the iron strip to ring the bell; it is the BREAKING of the contact (as the iron strip moves) that temporarily interrupts the circuit.
Option (d) Melts the coil — Incorrect: In normal operation, the electromagnet does not melt the coil. The coil is designed to handle the current flowing through it safely.
SSC GD 2026 – 7 May 2026 Shift 1 · Force on a current-carrying conductor and Fleming's left-hand rule

Q47. Two long parallel wires carry current in the same direction. What happens between them?

  1. (a) They repel each other
  2. (b) They attract each other
  3. (c) They remain unaffected
  4. (d) They oscillate
Answer & solution

Answer: (b) They attract each other

Correct Answer: They attract each other — Option (b)
When two long parallel wires carry current in the same direction, they attract each other. This is explained by Ampere's Force Law: each current-carrying wire produces a magnetic field around it. The magnetic field of one wire exerts a force on the current in the other wire. When currents flow in the same direction, the magnetic forces between the wires are directed towards each other — creating attraction. When currents flow in opposite directions, the wires repel each other. This principle is used to define the SI unit of current (Ampere).
Option (a) They repel each other — Incorrect: Parallel wires with currents in the SAME direction attract; repulsion occurs when currents flow in OPPOSITE directions.
Option (c) They remain unaffected — Incorrect: Current-carrying wires create magnetic fields that exert measurable forces on each other; they are never unaffected.
Option (d) They oscillate — Incorrect: The force between parallel current-carrying wires is constant (not oscillating) for steady direct currents; they do not oscillate.
SSC GD 2026 – 7 May 2026 Shift 3 · Force on a current-carrying conductor and Fleming's left-hand rule

Q48. According to Fleming's Left Hand Rule, which of the following is represented by the second finger (middle finger) of the left hand?

  1. (a) Direction of electric current
  2. (b) Direction of magnetic field
  3. (c) Force acting on the conductor
  4. (d) Measurement of resistance
Answer & solution

Answer: (a) Direction of electric current

Correct Answer: Direction of electric current — Option (a)
Fleming's Left Hand Rule is used to find the direction of force on a current-carrying conductor placed in a magnetic field. The rule states: Hold the forefinger (index finger), middle finger (second finger), and thumb of the left hand mutually perpendicular to each other. The forefinger points in the direction of the magnetic field (B); the middle finger (second finger) points in the direction of the electric current (I); the thumb points in the direction of the force (F) or motion of the conductor. This rule is used in electric motors.
Option (b) Direction of magnetic field — Incorrect: The forefinger (index/first finger) represents the direction of the magnetic field in Fleming's Left Hand Rule, not the middle finger.
Option (c) Force acting on the conductor — Incorrect: The thumb represents the direction of force/motion of the conductor in Fleming's Left Hand Rule.
Option (d) Measurement of resistance — Incorrect: Resistance is not represented by any finger in Fleming's Left Hand Rule; the rule deals with current, magnetic field, and force directions.
SSC GD 2026 – 28 April 2026 Shift 1 · Earth's magnetism

Q49. Earth's magnetic field protects us from charged solar particles. What happens when Earth's magnetic field temporarily weakens?

  1. (a) Increase in polar aurora and radiation exposure
  2. (b) Complete loss of the atmosphere
  3. (c) Increase in gravity
  4. (d) No effect
Answer & solution

Answer: (a) Increase in polar aurora and radiation exposure

Correct Answer: Increase in polar aurora and radiation exposure — Option (a)
Earth's magnetosphere (generated by the movement of molten iron in the outer core) acts as a protective shield, deflecting charged particles from the solar wind. When the magnetic field temporarily weakens (as happens during geomagnetic storms or polarity reversals), more solar particles penetrate into the atmosphere near the polar regions, causing: (1) Increased and more widespread polar auroras (Aurora Borealis in the north, Aurora Australis in the south) as solar particles interact with atmospheric gases; (2) Increased radiation exposure at higher altitudes and latitudes — posing risks to astronauts, airline passengers, and satellites; (3) Disruption of radio communications and GPS signals; (4) Potential damage to power grids due to geomagnetically induced currents. Such events, while spectacular for aurora watchers, can have significant technological and biological impacts.
Option (b) Complete loss of the atmosphere — Incorrect: A temporary weakening of the magnetic field does not cause complete atmospheric loss; this is an extreme scenario associated with complete and permanent loss of magnetosphere over geological timescales, not temporary weakening.
Option (c) Increase in gravity — Incorrect: Earth's gravity is determined by its mass and is independent of its magnetic field; a weakening of the magnetic field has no effect on gravitational force.
Option (d) No effect — Incorrect: A weakening of Earth's magnetic field has definite observable effects, primarily increased polar auroras, higher radiation exposure, and disruption of satellite communications and power infrastructure.
RRB NTPC GL CBT-1 2025-26 – 18 March 2026 Shift 1 · Earth's magnetism

Q50. Which layer of the Earth plays the primary role in generating the planet’s magnetic field?

  1. (a) Mantle
  2. (b) Crust
  3. (c) Outer core
  4. (d) Inner core
Answer & solution

Answer: (c) Outer core

Earth's Magnetic Field Generation
The outer core is liquid iron-nickel layer.
Convection currents in this molten metal create electric currents.
These electric currents generate Earth's magnetic field ( geodynamo effect).
Inner core: solid, no fluid motion.
Mantle & Crust: non-metallic, cannot generate magnetic field.
Answer: Option 3 → Outer core
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 2 · Solenoid and electromagnet

Q51. A strong magnetic field produced inside a solenoid can be used to magnetise a piece of soft iron placed inside the coil. The resulting magnet is called a/an __________.

  1. (a) Permanent magnet
  2. (b) Toroid
  3. (c) Natural magnet
  4. (d) Electromagnet
Answer & solution

Answer: (d) Electromagnet

The magnetic field inside a solenoid is strong and uniform.
When a piece of soft iron is placed inside this coil, it becomes magnetised due to the induced magnetic field.
This magnet produced by electric current in the coil and the soft iron inside is called an electromagnet.
Therefore, the correct answer is Electromagnet.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 2 · Force on a current-carrying conductor and Fleming's left-hand rule

Q52. In Fleming’s Left Hand Rule, which finger represents the direction of the magnetic field?

  1. (a) First (index) finger
  2. (b) Middle finger
  3. (c) Little finger
  4. (d) Thumb
Answer & solution

Answer: (a) First (index) finger

The Fleming's Left Hand Rule helps find the direction of force, magnetic field, and current in an electric motor.
According to the rule:
- The First finger (index finger) points at the direction of magnetic field.
- The seCond finger (middle finger) points at direction of current.
- The thuMb points at direction of motion or force.
Here, the question asks for the magnetic field direction, which is the First finger, i.e. index finger.
But from options, the magnetic field direction is represented by the First (index) finger.
Final answer: Option 1
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 3 · Force on a current-carrying conductor and Fleming's left-hand rule

Q53. A wire carrying current is placed between the poles of a magnet. It experiences maximum force when it _____.

  1. (a) is outside the magnetic field
  2. (b) is perpendicular to the magnetic field
  3. (c) is parallel to the magnetic field
  4. (d) is at 45° to the magnetic field
Answer & solution

Answer: (b) is perpendicular to the magnetic field

A current-carrying wire in a magnetic field experiences a force given by the Lorentz force law.
The magnitude of force is maximum when the wire is perpendicular to the magnetic field.
This is because force F = I L B sin θ, where θ is the angle between wire and magnetic field.
Sin 90° = 1, the maximum value, so maximum force occurs at 90°, i.e., perpendicular orientation.
Therefore, the wire experiences maximum force when it is perpendicular to the magnetic field.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 1 · Force on a current-carrying conductor and Fleming's left-hand rule

Q54. The magnitude of force on a conductor in a magnetic field increases when _______.

  1. (a) Current increases
  2. (b) Length decreases
  3. (c) Magnetic field decreases
  4. (d) Current decreases
Answer & solution

Answer: (a) Current increases

The force on a conductor in a magnetic field is given by the formula:
F = BIL sin θ, where F is force, B is magnetic field strength, I is current, L is length of conductor, and θ is angle.
From the formula, force is directly proportional to the current flowing through the conductor.
Increasing current increases the force acting on the conductor.
Therefore, the force increases when the current increases.
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 3 · Force on a moving charge in a magnetic field

Q55. A charged particle moves perpendicular to the axis of a circular current loop. The force on the particle is ________.

  1. (a) Constant everywhere
  2. (b) Maximum at center
  3. (c) Depends on position and velocity
  4. (d) Always zero
Answer & solution

Answer: (c) Depends on position and velocity

The charged particle moving perpendicular to the axis of a circular current loop experiences a magnetic force.
The magnetic field created by the loop varies with position.
The force depends on both the particle's velocity and its position in the magnetic field.
Hence, the force is not constant, not always zero, and not simply maximum at the center.
The correct answer is that the force depends on position and velocity.
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 2 · Force on a current-carrying conductor and Fleming's left-hand rule

Q56. Which of the following is true about Fleming’s left-hand rule?

  1. (a) If the thumb points in the direction of force and the forefinger in the direction of current, the middle finger shows the direction of magnetic field.
  2. (b) It is used only in electric circuits and not in devices like motors or loudspeakers.
  3. (c) If the thumb points in the direction of current and the middle finger in the direction of magnetic field, the forefinger shows the direction of force.
  4. (d) If the forefinger points in the direction of magnetic field and the middle finger in the direction of current, the thumb shows the direction of motion or force on the conductor.
Answer & solution

Answer: (d) If the forefinger points in the direction of magnetic field and the middle finger in the direction of current, the thumb shows the direction of motion or force on the conductor.

Fleming's left-hand rule is used to find the direction of force (motion) on a current-carrying conductor in a magnetic field.
According to the rule:
- The forefinger points in the direction of the magnetic field (North to South).
- The middle finger points in the direction of the current.
- The thumb points in the direction of the force (motion) on the conductor.
Option 4 correctly states this relationship.
Other options either mix the directions or state incorrect uses of the rule.
Hence, the correct option is 4.
This rule is fundamental in devices like motors and loudspeakers, where force direction is important.
Final answer: Option 4
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 1 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q57. Which of the following statement(s) is/are true regarding the magnetic field line pattern around a straight current carrying wire?
(i) The magnetic field lines around a current carrying wire are in the form of concentric circles.
(ii) The magnetic field lines around a current carrying wire intersect at various points.
(iii) The magnetic field lines move farther apart as one moves away from the wire.

  1. (a) Both (ii) and (iii)
  2. (b) Only (ii)
  3. (c) Only (i)
  4. (d) Both (i) and (iii)
Answer & solution

Answer: (d) Both (i) and (iii)

Magnetic field lines around a straight current carrying wire form concentric circles around the wire (True for statement i).
Magnetic field lines never intersect because that would mean two different directions of the magnetic field at a single point (False for statement ii).
As you move away from the wire, the magnetic field strength decreases, so the field lines move farther apart (True for statement iii).
Thus, statements (i) and (iii) are true and (ii) is false.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 1 · Domestic electric circuits, fuse and earthing

Q58. A technician needs to connect a new appliance in a domestic circuit to ensure it receives full voltage and can be operated independently. What should the technician do?

  1. (a) Connect the appliance only to the neutral wire
  2. (b) Connect the appliance in parallel with existing appliances
  3. (c) Connect the appliance in series with existing appliances
  4. (d) Connect the appliance only to the earth wire
Answer & solution

Answer: (b) Connect the appliance in parallel with existing appliances

Correct answer: Option 2
In a domestic circuit, appliances must receive full voltage independently.
Connecting the appliance in parallel ensures it gets full voltage.
Series connection divides voltage among appliances, so not suitable.
Connection to neutral or earth alone won't power the appliance.
Therefore, connect the appliance in parallel with existing ones.
This is standard practice for household wiring.
This ensures safety and proper operation.
Answer complete.
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 2 · Domestic electric circuits, fuse and earthing

Q59. What role does the earth wire play in the safety of domestic appliances with metallic bodies?

  1. (a) It prevents the fuse from melting
  2. (b) It controls the current flow
  3. (c) It increases the appliance's voltage
  4. (d) It provides a low-resistance path for leakage current
Answer & solution

Answer: (d) It provides a low-resistance path for leakage current

The earth wire in domestic appliances is connected to the metallic body.
It provides a low-resistance path to the ground for any leakage current.
This prevents electric shock to the user if the live wire touches the metal body.
Hence, it enhances safety by directing leakage current safely to the earth.
So, the earth wire's main role is to provide a low-resistance path for leakage current.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 3 · Solenoid and electromagnet

Q60. Which material can be magnetised using the strong magnetic field inside a solenoid?

  1. (a) Aluminum
  2. (b) Plastic
  3. (c) Copper
  4. (d) Soft iron
Answer & solution

Answer: (d) Soft iron

Soft iron can be magnetised by placing it inside a strong magnetic field such as inside a solenoid.
This is because soft iron is a ferromagnetic material that easily gains magnetic properties when subjected to an external magnetic field.
Materials like aluminum, plastic, and copper are not easily magnetised as they are paramagnetic or diamagnetic and do not retain magnetism.
Therefore, the correct choice is soft iron.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 1 · Force on a current-carrying conductor and Fleming's left-hand rule

Q61. Which rule helps to determine the direction of force acting on a current-carrying conductor in a magnetic field?

  1. (a) Fleming's left-hand rule
  2. (b) Faraday's law
  3. (c) Ampere's rule
  4. (d) Right-hand rule
Answer & solution

Answer: (a) Fleming's left-hand rule

The question asks which rule determines the direction of force on a current-carrying conductor in a magnetic field.
Fleming's left-hand rule is used to find the direction of force on the conductor.
In this rule, the thumb indicates the direction of force, the forefinger the magnetic field, and the middle finger the current.
Other options like Faraday's law relate to electromagnetic induction, Ampere's rule is for magnetic field direction, and the right-hand rule is commonly used for different magnetic phenomena.
Hence, Fleming's left-hand rule is the correct choice.
Final answer: Option 1
SSC MTS 2025 – 19 February 2026 Shift 2 · Domestic electric circuits, fuse and earthing

Q62. In India, which of the following colour is used to denote the earth wire in the supply?

  1. (a) White
  2. (b) Red
  3. (c) Green
  4. (d) Black
Answer & solution

Answer: (c) Green

The correct answer is option 3.
In India's electrical supply system (as per IS standards and IEC conventions):
Green (or Green with Yellow stripe) — Earth wire (protective ground)
Red (or Brown in newer standards) — Live wire (phase)
Black (or Blue in newer standards) — Neutral wire
The earth wire is connected to the ground for safety, providing a path for fault current and protecting users from electric shock. Green is the universally recognized colour for the earth/ground wire.
Option 1 is incorrect: White is not used for the earth wire in India's electrical system.
Option 2 is incorrect: Red denotes the live (phase) wire in the older Indian electrical standard.
Option 4 is incorrect: Black denotes the neutral wire, not the earth wire.
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 3 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q63. A student observes that a compass needle deflects when brought near a current-carrying wire. Using your understanding of magnetic fields, explain why this happens.

  1. (a) A current-carrying wire creates a magnetic field that exerts a force on the compass needle.
  2. (b) The wire produces an electric force that acts on the compass needle.
  3. (c) The wire heats up, causing air currents to move the needle.
  4. (d) The wire causes a gravitational effect moving the needle.
Answer & solution

Answer: (a) A current-carrying wire creates a magnetic field that exerts a force on the compass needle.

A current flowing through a wire generates a magnetic field around it.
The compass needle aligns itself with the surrounding magnetic field.
When the wire is near the compass, the magnetic field from the wire influences the needle.
This causes the needle to deflect from Earth's magnetic field direction and point according to the wire's field.
Hence, the deflection is due to the magnetic field created by the current in the wire.
Final answer: Option 1
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 1 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q64. How does the magnetic field strength at the center of a circular loop change if the current through the loop is doubled?

  1. (a) It becomes half as large
  2. (b) It becomes twice as large
  3. (c) It remains unchanged
  4. (d) It becomes four times as large
Answer & solution

Answer: (b) It becomes twice as large

Magnetic field strength (B) at the centre of a circular current loop is directly proportional to the current (I) flowing through it.
Formula: B ∝ I
If the current is doubled, the magnetic field strength also doubles.
Therefore, if current I becomes 2I, magnetic field B becomes 2B.
Hence, magnetic field strength becomes twice as large.
Final answer: Option 2
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q65. Which of the following arrangements produces a nearly uniform magnetic field in the central region of a circular current-carrying system under steady conditions?

  1. (a) Arranging loops in random orientations
  2. (b) Allowing current to vary with time in a single loop
  3. (c) Using multiple closely wound turns of identical radius with constant current
  4. (d) Using loops of varying radii
Answer & solution

Answer: (c) Using multiple closely wound turns of identical radius with constant current

The most uniform magnetic field in the central region is produced when multiple loops are arranged.
Specifically, multiple closely wound turns of identical radius create nearly uniform magnetic fields by adding their effects.
Random orientations or varying radii distort the uniformity of the field.
Time-varying current in a single loop does not produce a steady uniform magnetic field.
Therefore, using multiple closely wound turns with constant current is the best choice for uniformity.
Final answer: Option 3
SSC MTS 2025 – 18 February 2026 Shift 3 · Solenoid and electromagnet

Q66. Which of the following is a correct use of electromagnets?
I. In separating magnetic material from junk
II. In sharpening pencils

  1. (a) Only I
  2. (b) Only II
  3. (c) Both I and II
  4. (d) Neither I nor II
Answer & solution

Answer: (a) Only I

The correct answer is option 1.
Electromagnets are used in separating magnetic material (like iron and steel scraps) from junk in scrap yards. Large industrial electromagnets can pick up and move heavy metallic scrap, making them very useful in recycling and waste management industries. This is a well-known practical application of electromagnets.
Statement II is incorrect: Sharpening pencils involves a purely mechanical cutting action and has absolutely no connection to electromagnets or magnetism.
Option 2 is incorrect: 'Only II' would mean only pencil sharpening uses electromagnets, which is completely wrong.
Option 3 is incorrect: 'Both I and II' would include sharpening pencils, which is not a use of electromagnets.
Option 4 is incorrect: 'Neither I nor II' would deny that electromagnets separate magnetic material from junk, which is a well-established fact.
Delhi Police Head Constable (Ministerial) 2025-26 – 8 January 2026 Shift 3 · Electric generator and Fleming's right-hand rule

Q67. Which of the following statements about electric generators is/are correct?
I. They work on electromagnetic induction.
II. AC generators use slip rings.
III. DC generators use a split-ring commutator.

  1. (a) I only
  2. (b) I and II only
  3. (c) I and III only
  4. (d) I, II and III all are correct
Answer & solution

Answer: (d) I, II and III all are correct

Correct Answer: Option 4 – I, II and III all are correct
Statement I is CORRECT: All electric generators — both AC and DC — work on the principle of electromagnetic induction (Faraday's Law). When a coil rotates in a magnetic field, an EMF is induced.
Statement II is CORRECT: AC generators (alternators) use slip rings (also called collector rings) to connect the rotating coil to the external circuit. Slip rings allow continuous rotation, which produces alternating current.
Statement III is CORRECT: DC generators use a split-ring commutator (commutator ring). The commutator reverses the connection of the coil to the external circuit every half rotation, converting the alternating EMF generated inside the coil into a unidirectional (DC) output.
All three statements are factually accurate and correct.
Delhi Police Constable (Exe) 2025-26 – 5 January 2026 Shift 2 · Magnetic materials (dia, para, ferro)

Q68. Which of the following is an example of a paramagnetic material that is weakly attracted to an external magnetic field?

  1. (a) Iron
  2. (b) Aluminium
  3. (c) Lead
  4. (d) Copper
Answer & solution

Answer: (b) Aluminium

The correct answer is (b) Aluminium .
Aluminium is a paramagnetic material — it has unpaired electrons that cause it to be weakly attracted to an external magnetic field. Paramagnetic materials have a small, positive magnetic susceptibility.
(a) Iron: Iron is a ferromagnetic material — it has strong, permanent magnetic properties and is strongly attracted to magnets. Not paramagnetic.
(c) Lead: Lead is a diamagnetic material — it is weakly repelled by magnetic fields, not attracted.
(d) Copper: Copper is also a diamagnetic material — it is weakly repelled by an external magnetic field.
Delhi Police Constable (Exe) 2025-26 – 23 December 2025 Shift 3 · Earth's magnetism

Q69. What is the approximate ratio of Earth's magnetic field strength at the equator compared to the poles?

  1. (a) 1:1
  2. (b) 1:2
  3. (c) 1:3
  4. (d) 1:4
Answer & solution

Answer: (b) 1:2

The correct answer is 1:2 (Option 2).
The Earth's magnetic field is stronger at the poles than at the equator. The approximate ratio of the magnetic field strength at the equator to the poles is 1:2, meaning the field at the poles is about twice as strong as at the equator. This is because the magnetic field lines are more concentrated and nearly vertical at the poles.
Option 1 - 1:1: A ratio of 1:1 would mean equal magnetic field strength at both the equator and the poles, which is not the case.
Option 3 - 1:3: A ratio of 1:3 would imply the poles have three times stronger field than the equator, which overestimates the difference.
Option 4 - 1:4: A ratio of 1:4 would imply four times stronger field at poles than at equator, which is a significant overestimate.
SSC Stenographer 2025 – 8 December 2025 Shift 3 · Electromagnetic induction and Faraday's laws

Q70. According to Lenz’s Law, what determines the direction of an induced current in a conductor?

  1. (a) It flows to oppose the variation in magnetic flux causing it.
  2. (b) It continuously reduces the applied magnetic flux.
  3. (c) It is proportional to the strength of the magnetic field.
  4. (d) It always enhances the existing magnetic field.
Answer & solution

Answer: (a) It flows to oppose the variation in magnetic flux causing it.

[IMAGE: SSC Steno GK (eng)_image_10.png]
SSC Stenographer 2025 – 6 December 2025 Shift 1 · Electromagnetic induction and Faraday's laws

Q71. A conductor rod moving with a velocity v perpendicular to a uniform magnetic field B. If the length of the rod perpendicular to both v and B is L, the induced EMF across its ends is given by?

  1. (a) BLv
  2. (b) BL²v
  3. (c) Bv /L
  4. (d) B/√L
Answer & solution

Answer: (a) BLv

The correct answer is BLv . According to Faraday’s law of electromagnetic induction , the induced EMF (ε) in a conductor moving in a magnetic field is given by: ε = B × L × v Here, B = magnetic field strength L = length of the conductor v = velocity of the conductor (perpendicular to both L and B) The derivation comes from the formula: ε = dΦ /dt = B × A/time , where the rate of change of magnetic flux (Φ) leads to induced EMF. Since the rod sweeps an area (A = L × displacement), and displacement/time = velocity, the formula reduces to ε = BLv . This principle is the working foundation of devices like electric generators, railguns, and electromagnetic brakes .
SSC Stenographer 2025 – 6 December 2025 Shift 2 · Electromagnetic induction and Faraday's laws

Q72. At what orientation does a rotating coil in a uniform magnetic field generate the maximum induced EMF?

  1. (a) When the coil’s plane is at 45° to the magnetic field lines
  2. (b) When the magnetic flux through the coil is maximum
  3. (c) When the coil’s plane is parallel to the magnetic field lines
  4. (d) When the coil’s plane is perpendicular (90°) to the magnetic field lines
Answer & solution

Answer: (c) When the coil’s plane is parallel to the magnetic field lines

[IMAGE: SSC Steno GK (eng)_image_11.png]
SSC CGL Tier-1 2025 – 19 September 2025 Shift 3 · Earth's magnetism

Q73. Which phenomenon is primarily responsible for auroras near Earth's poles?

  1. (a) Earthquake waves
  2. (b) Lightning discharges
  3. (c) Solar wind and magnetic field interaction
  4. (d) Volcanic ash dispersion
Answer & solution

Answer: (c) Solar wind and magnetic field interaction

Auroras (Northern and Southern Lights) occur when charged particles from the solar wind interact with Earth's magnetic field and excite atmospheric gases near the poles.
The interaction produces the characteristic glowing lights.
Hence Option 3 is correct.
SSC CGL Tier-1 2025 – 16 September 2025 Shift 1 · Solenoid and electromagnet

Q74. Which of the following pairs is correctly matched regarding electromagnetic devices?

  1. (a) Electric Generator : Converts electrical energy to mechanical energy.
  2. (b) Transformer : Operates on DC current to change voltage.
  3. (c) Electromagnet : A permanent magnet.
  4. (d) Electric Bell : Uses the magnetic effect of electric current.
Answer & solution

Answer: (d) Electric Bell : Uses the magnetic effect of electric current.

Generator converts mechanical energy to electrical energy, not the reverse.
Transformer operates on AC, not DC.
Electromagnet is a temporary magnet activated by current, not a permanent one.
Electric bell uses the magnetic effect of electric current – correctly matched.
RRB NTPC UG CBT-1 2024-25 – 8 September 2025 Shift 1 · Magnetic field and field lines

Q75. What does the closeness of magnetic field lines indicate about the magnetic field?

  1. (a) Direction of the electric field
  2. (b) Direction of the magnetic field
  3. (c) Relative strength of the magnetic field
  4. (d) Presence of electric charge
Answer & solution

Answer: (c) Relative strength of the magnetic field

RRB NTPC UG CBT-1 2024-25 – 8 September 2025 Shift 2 · Electromagnetic induction and Faraday's laws

Q76. According to Lenz’s Law, the direction of induced current is such that _________.

  1. (a) it aids the change in magnetic flux
  2. (b) it opposes the change in magnetic flux
  3. (c) it strengthens the applied magnetic field
  4. (d) it neutralises the magnetic field completely
Answer & solution

Answer: (b) it opposes the change in magnetic flux

RRB NTPC UG CBT-1 2024-25 – 3 September 2025 Shift 3 · Electromagnetic induction and Faraday's laws

Q77. What is self-induction?

  1. (a) Induction of EMF in one coil due to a current in a nearby coil
  2. (b) Induction of EMF in a coil due to motion in a magnetic field
  3. (c) Induction of EMF in a coil due to a change in its own current
  4. (d) Generation of current in a coil due to temperature changes
Answer & solution

Answer: (c) Induction of EMF in a coil due to a change in its own current

RRB NTPC UG CBT-1 2024-25 – 14 August 2025 Shift 1 · Force on a moving charge in a magnetic field

Q78. What can be the shape of the trajectory of a charged particle moving in a uniform magnetic field?

  1. (a) Hyperbolic path
  2. (b) Helical path
  3. (c) Parabolic path
  4. (d) Elliptical path
Answer & solution

Answer: (b) Helical path

RRB NTPC UG CBT-1 2024-25 – 7 August 2025 Shift 2 · Force on a moving charge in a magnetic field

Q79. Which of the following quantities remains unchanged when a charged particle moves in a magnetic field?

  1. (a) Direction of velocity
  2. (b) Kinetic energy
  3. (c) Momentum direction
  4. (d) Angular momentum
Answer & solution

Answer: (b) Kinetic energy

SSC Selection Post 2025 (Phase XIII) – 30 July 2025 Shift 2 · AC, DC and transformer

Q80. To modify the magnitude of an alternating voltage without altering its frequency, which principle is applied in the functioning of a transformer?

  1. (a) Self-induction
  2. (b) Electromagnetic radiation
  3. (c) Mutual induction
  4. (d) Capacitive coupling
Answer & solution

Answer: (c) Mutual induction

Correct Answer: Option 3 – Mutual induction
A transformer works on the principle of mutual induction (electromagnetic induction between two coils). When alternating current flows through the primary coil, it creates a changing magnetic flux in the iron core. This changing flux links with the secondary coil and induces an alternating EMF in it (Faraday's Law). The ratio of voltages equals the ratio of turns: V₁/V₂ = N₁/N₂. The frequency remains unchanged (same AC frequency from primary to secondary) while voltage magnitude changes. Step-up transformers increase voltage; step-down transformers decrease voltage.
Option 1 (Self-induction): Self-induction is when a changing current in a coil induces an EMF in the SAME coil — not between two separate coils. Relevant to inductors, not transformers.
Option 2 (Electromagnetic radiation): Refers to radiated EM waves (light, radio waves) propagating through space — not the near-field inductive coupling principle of transformers.
Option 4 (Capacitive coupling): Uses electric field between capacitor plates to transfer energy — a different mechanism, not used in standard transformers.
RRB NTPC GL CBT-1 2024-25 – 12 June 2025 Shift 2 · Magnetic materials (dia, para, ferro)

Q81. What happens to magnetic fields when a material becomes superconducting and experiences the Meissner effect?

  1. (a) Magnetic fields are increased in strength within the material.
  2. (b) Magnetic fields are completely expelled from the interior of the material.
  3. (c) Magnetic fields are absorbed and stored inside the material.
  4. (d) Magnetic fields penetrate the material freely.
Answer & solution

Answer: (b) Magnetic fields are completely expelled from the interior of the material.

RRB NTPC GL CBT-1 2024-25 – 9 June 2025 Shift 3 · Magnetic materials (dia, para, ferro)

Q82. The Meissner effect is a defining characteristic of which state of matter?

  1. (a) Insulating state
  2. (b) Paramagnetic state
  3. (c) Ferromagnetic state
  4. (d) Superconducting state
Answer & solution

Answer: (d) Superconducting state

RRB Technician Grade III 2024-25 – 30 December 2024 Shift 1 · Magnetic field and field lines

Q83. When iron filings are sprinkled around a magnet, they form a pattern. What does this pattern represent?

  1. (a) Both electric and magnetic field lines
  2. (b) Electric field lines
  3. (c) Magnetic field lines
  4. (d) Neither electric nor magnetic field lines
Answer & solution

Answer: (c) Magnetic field lines

Correct Answer: Option 3 — Magnetic field lines
Each iron filing is a tiny piece of soft iron. Placed near a magnet it becomes a small induced magnet and turns until it points along the direction of the magnetic field at that spot. Thousands of such filings line up end to end and trace out curved chains — these chains are the magnetic field lines (also called lines of force) of the magnet.
The pattern shows that the field is strongest at the two poles, where the filings crowd most densely, and weaker in the middle. Outside the magnet every line runs from the North pole to the South pole, and inside the magnet it continues from South to North, so the lines form closed loops. Two field lines can never intersect, because at a crossing point the compass needle would have to point in two directions at once.
❌ Why the other options are incorrect
✗ Both electric and magnetic field lines — a bar magnet carries no net charge, so it produces no electric field; only the magnetic pattern appears.
✗ Electric field lines — these are produced by electric charges and are mapped with a test charge, not with iron filings.
✗ Neither electric nor magnetic field lines — the pattern is the standard classroom demonstration of a magnetic field, so this is plainly wrong.
📌 SSC & Railway Exam Facts
• Magnetic field is a vector quantity; SI unit tesla (T); CGS unit gauss; 1 T = 10⁴ gauss.
• Field lines are closed, continuous curves; they never cross each other.
• Closer the field lines, stronger the field — hence maximum crowding at the poles.
• The direction of the field at a point is the direction in which the north pole of a compass points there.
• Magnetic field lines were introduced by Michael Faraday.
RRB Technician Grade III 2024-25 – 30 December 2024 Shift 1 · Force on a current-carrying conductor and Fleming's left-hand rule

Q84. Which of the following device is governed by Flemming's Left Hand Rule

  1. (a) Electric Iron
  2. (b) Electric Bulb
  3. (c) Electric Geyser
  4. (d) Electric motor
Answer & solution

Answer: (d) Electric motor

Correct Answer: Option 4 — Electric motor
Fleming's Left Hand Rule gives the direction of the force on a current-carrying conductor placed in a magnetic field. Stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular: the Forefinger points along the magnetic Field, the Middle finger along the Current, and then the Thumb gives the direction of Thrust (force / motion).
An electric motor works on exactly this principle. A current-carrying coil placed in a magnetic field experiences equal and opposite forces on its two arms; this pair of forces forms a couple that makes the coil rotate, converting electrical energy into mechanical energy. A split-ring commutator reverses the current every half turn so that the rotation continues in the same sense.
❌ Why the other options are incorrect
✗ Electric Iron — works on the heating effect of current (Joule's law, H = I²Rt), using a nichrome heating element.
✗ Electric Bulb — also the heating effect: a tungsten filament is heated until it glows white hot.
✗ Electric Geyser — again the heating effect, with a resistive coil warming the water.
📌 SSC & Railway Exam Facts
• Fleming's Left Hand Rule → motor (force on a current-carrying conductor).
• Fleming's Right Hand Rule → generator / dynamo (induced current, electromagnetic induction).
• Force on a conductor: F = BIL sin θ; maximum when the conductor is perpendicular to the field.
• A motor converts electrical → mechanical energy; a generator converts mechanical → electrical.
• Electromagnetic induction was discovered by Michael Faraday; the right-hand thumb rule gives the field direction around a straight current.
RRB Technician Grade III 2024-25 – 30 December 2024 Shift 2 · Domestic electric circuits, fuse and earthing

Q85. Which of the following statements is true for the appliances used in domestic circuits:

  1. (a) Heavy appliances like AC, Geyser are connected in series and light appliances like bulbs, tubelights are connected in parallel
  2. (b) Heavy appliances like AC, Geyser are connected in parallel and light appliances like bulbs, tubelights are connected in series
  3. (c) All the appliances are connected in parallel
  4. (d) All the appliances are connected in series
Answer & solution

Answer: (c) All the appliances are connected in parallel

Correct Answer: Option 3 — All the appliances are connected in parallel
In every domestic wiring circuit each appliance is connected in parallel across the live and neutral wires. There are three solid reasons for this.
First, a parallel connection gives every appliance the same full voltage of 220 V, which is the voltage each one is designed for. In a series circuit the supply voltage would be shared out, and no device would get its rated voltage.
Second, each appliance can be switched on or off independently, and if one of them fuses the others keep working, because the other paths are still complete.
Third, parallel connection lets each appliance draw the current it needs according to I = V/R, so a 2000 W geyser and a 10 W LED can run side by side on the same line.
❌ Why the other options are incorrect
✗ Heavy appliances in series, light appliances in parallel — putting an AC or geyser in series would drop its voltage below 220 V and it would not work properly.
✗ Heavy appliances in parallel, light appliances in series — bulbs in series would glow dim, and a single fused bulb would switch off the whole lighting line.
✗ All the appliances are connected in series — the same current would flow through every device, the total resistance would rise, and one failure would kill the entire house circuit.
📌 SSC & Railway Exam Facts
• Domestic supply in India: 220 V, 50 Hz AC.
• Wire colours: live — red/brown, neutral — black/blue, earth — green.
• The fuse is always connected in the live wire, in series with the circuit.
• Earth wire carries leakage current safely to the ground and prevents electric shock from metallic bodies.
• Separate circuits are used for lights (5 A) and heavy appliances (15 A).
RRB Technician Grade III 2024-25 – 30 December 2024 Shift 2 · Force on a current-carrying conductor and Fleming's left-hand rule

Q86. The force experienced by a current carrying conductor in a magnetic field is maximum when the angle between the direction of current and the direction of magnetic field is

  1. (a) 60°
  2. (b) 0°
  3. (c) 45°
  4. (d) 90°
Answer & solution

Answer: (d) 90°

Correct Answer: Option 4 — 90°
The force on a straight conductor of length L carrying current I placed in a magnetic field B is
F = BIL sin θ
where θ is the angle between the direction of the current and the direction of the magnetic field. The force therefore depends on sin θ, and sin θ reaches its greatest value of 1 at θ = 90°. So the force is maximum, F = BIL, when the current flows perpendicular to the magnetic field.
Conversely, when the conductor lies parallel or antiparallel to the field, θ = 0° or 180°, sin θ = 0 and the force is zero. The direction of this force is given by Fleming's left-hand rule, and it is the principle behind the electric motor.
❌ Why the other options are incorrect
✗ 60° — sin 60° = 0.866, so the force is 86.6% of the maximum, large but not the largest.
✗ 0° — sin 0° = 0; here the conductor is along the field and experiences no force at all. This is the minimum, the exact opposite of what is asked.
✗ 45° — sin 45° = 0.707, giving only about 71% of the maximum force.
📌 SSC & Railway Exam Facts
• F = BIL sin θ; maximum at θ = 90° (F = BIL), zero at θ = 0°.
• Fleming's left-hand rule gives the direction of force on a current-carrying conductor — used in the electric motor.
• Fleming's right-hand rule gives the direction of induced current — used in the generator.
• SI unit of magnetic field B is the tesla (T); 1 T = 1 N A⁻¹ m⁻¹.
• Force on a moving charge: F = qvB sin θ; a charge moving along B feels no magnetic force.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q87. What is the direction of the magnetic field produced by a current carrying straight wire?

  1. (a) At an angle 45° to the plane of the wire
  2. (b) Parallel to the plane of the wire
  3. (c) At an angle 60° to the plane of the wire
  4. (d) Perpendicular to the plane of the wire
Answer & solution

Answer: (d) Perpendicular to the plane of the wire

Correct Answer: Option 4 — Perpendicular to the plane of the wire
When a current flows through a straight conductor, it produces a magnetic field around itself. The field lines are concentric circles with the wire at their centre, and these circles lie in a plane perpendicular to the wire. So at every point the magnetic field is perpendicular to the wire and tangential to the circle passing through that point.
The sense (clockwise or anticlockwise) is given by Maxwell's Right-Hand Thumb Rule: hold the wire in your right hand with the thumb pointing along the current; the curled fingers then show the direction of the magnetic field lines.
The strength of the field is given by B ∝ I/r — it increases with current I and decreases as the distance r from the wire increases. That is why the circles are drawn crowded close to the wire and far apart away from it.
This effect was discovered accidentally by Hans Christian Oersted (1820), when a compass needle near a current-carrying wire deflected.
❌ Why the other options are incorrect
✗ At an angle 45° to the plane of the wire — the field is never at a fixed slant of 45°; the circular field lines always stay in the perpendicular plane.
✗ Parallel to the plane of the wire — if the field were parallel to the wire, a compass placed near it would not deflect sideways, which contradicts Oersted's experiment.
✗ At an angle 60° to the plane of the wire — an arbitrary angle with no physical meaning for a straight conductor.
📌 SSC & Railway Exam Facts
• Oersted (1820) first showed that electricity produces magnetism; SI unit of magnetic field strength H is named oersted in CGS.
• SI unit of magnetic flux density B is the tesla (T); 1 T = 1 Wb m⁻².
• Right-Hand Thumb Rule (also called Maxwell's corkscrew rule) gives the direction of B around a straight wire.
• Inside a solenoid the field is uniform and parallel to the axis, like that of a bar magnet.
• Fleming's Left-Hand Rule → motor (force on a conductor); Fleming's Right-Hand Rule → generator (induced current).
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · Solenoid and electromagnet

Q88. Among the following cases, which kind of magnetic field production is found similar to the magnetic-field of a bar magnet?

  1. (a) A rectangular loop carrying current.
  2. (b) A solenoid of finite length carrying current.
  3. (c) A circular loop carrying current.
  4. (d) An infinitely long wire carrying current.
Answer & solution

Answer: (b) A solenoid of finite length carrying current.

Correct Answer: Option 2 — A solenoid of finite length carrying current.
A solenoid is a long coil made of many closely wound circular turns of insulated copper wire. When a current flows through it, the fields of all the turns add up.
The resulting pattern is exactly like that of a bar magnet: the field lines come out of one end and go into the other, so one end behaves as the north pole and the other as the south pole. Inside the solenoid the field lines are straight, parallel and equally spaced, which means the field there is strong and uniform, given by B = μ₀nI.
This is why a current-carrying solenoid is used to make an electromagnet — put a soft iron core inside it and the field becomes many times stronger. The polarity is found by the right-hand thumb rule or the clock rule.
❌ Why the other options are incorrect
✗ A rectangular loop carrying current. — a single loop of any shape gives a weak field that is not uniform and does not resemble the extended two-pole field of a bar magnet.
✗ A circular loop carrying current. — near its centre a single circular loop behaves somewhat like a tiny magnetic dipole, but its field is far weaker and much less uniform than a solenoid's.
✗ An infinitely long wire carrying current. — a straight wire produces concentric circular field lines around it, a pattern completely unlike a bar magnet; here B = μ₀I/2πr.
📌 SSC & Railway Exam Facts
• Field inside a long solenoid: B = μ₀nI, where n = number of turns per unit length.
• Field at the centre of a circular coil: B = μ₀nI/2r; around a straight wire: B = μ₀I/2πr.
• Magnetic field lines never intersect, and they always form closed loops.
• Oersted (1820) discovered the magnetic effect of electric current.
• An electromagnet uses a soft iron core (temporary magnet); a permanent magnet uses steel.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q89. The magnetic field due to a current carrying coil increases when:

  1. (a) One moves way from the coil
  2. (b) current through the coil is decreased
  3. (c) number of turns of the coil is decreased
  4. (d) current through the coil is increased
Answer & solution

Answer: (d) current through the coil is increased

Correct Answer: Option 4 — current through the coil is increased
The magnetic field produced at the centre of a current-carrying circular coil is given by
B = μ₀nI / 2r
where I is the current, n the number of turns, r the radius of the coil and μ₀ the permeability of free space.
From this relation, B is directly proportional to the current I and directly proportional to the number of turns n. So doubling the current doubles the field. Increasing the current is therefore the correct way to make the field stronger — this is exactly how the strength of an electromagnet is controlled.
❌ Why the other options are incorrect
✗ One moves way from the coil — the field of a coil weakens rapidly as the distance from it increases.
✗ current through the coil is decreased — since B ∝ I, reducing the current reduces the magnetic field.
✗ number of turns of the coil is decreased — since B ∝ n, fewer turns give a weaker field.
📌 SSC & Railway Exam Facts
• Field at the centre of a circular coil: B = μ₀nI / 2r; inside a long solenoid: B = μ₀nI.
• SI unit of magnetic field (flux density) is the tesla (T); CGS unit is the gauss; 1 T = 10⁴ gauss.
• Direction of the field is found by the Right-Hand Thumb Rule (Maxwell's corkscrew rule).
• Oersted discovered in 1820 that a current-carrying wire deflects a magnetic needle.
• An electromagnet is strengthened by more turns, more current and a soft iron core.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 2 · Solenoid and electromagnet

Q90. Which of the following statements is/are true about the field around a current carrying solenoid:
(i)The field inside the solenoid is uniform.
(ii) The field outside the solenoid is same in magnitude as the field inside the solenoid.
(iii) The field around the solenoid is similar to the field around a bar magnet.

  1. (a) Both (i) and (iii)
  2. (b) Both (ii) and (iii)
  3. (c) Only(i)
  4. (d) Only (iii)
Answer & solution

Answer: (a) Both (i) and (iii)

Correct Answer: Option 1 — Both (i) and (iii)
A solenoid is a long coil of many circular turns of insulated copper wire wound closely like a cylinder.
Statement (i) is TRUE — inside a long current-carrying solenoid the field lines are straight, parallel and equally spaced, so the magnetic field there is uniform, given by B = μ₀nI.
Statement (iii) is TRUE — the pattern of field lines outside a solenoid is exactly like that of a bar magnet. One end behaves as the north pole and the other as the south pole, which is why a current-carrying solenoid is called an electromagnet.
Statement (ii) is FALSE — the field outside a long solenoid is very weak (nearly zero), not equal to the strong uniform field inside.
❌ Why the other options are incorrect
✗ Both (ii) and (iii) — it wrongly includes (ii); the outside field is almost zero, not equal to the inside field.
✗ Only(i) — it leaves out the true statement (iii) about the bar-magnet-like pattern.
✗ Only (iii) — it leaves out the true statement (i) about the uniform field inside.
📌 SSC & Railway Exam Facts
• Field inside a long solenoid: B = μ₀nI, where n is the number of turns per unit length.
• A solenoid with a soft iron core becomes a powerful electromagnet.
• Magnetic field lines are closed curves; they never intersect each other.
• Outside a magnet, field lines run north to south; inside, they run south to north.
• Electromagnets are used in electric bells, cranes, loudspeakers and MRI machines.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 1 · Solenoid and electromagnet

Q91. Which of the following statement is NOT true for the magnetic field lines inside a current-carrying solenoid?

  1. (a) Ellipsoidal and intersects with each other
  2. (b) Uniform inside the solenoid
  3. (c) Along the axis and parallel to each other
  4. (d) The same at all points inside the solenoid
Answer & solution

Answer: (a) Ellipsoidal and intersects with each other

Correct Answer: Option 1 — Ellipsoidal and intersects with each other
Inside a current-carrying solenoid the magnetic field lines are straight, parallel to the axis, equally spaced and all in the same direction. Such a pattern means the field is uniform — the same in magnitude and direction at every interior point.
The statement that the lines are ellipsoidal and intersect with each other is therefore not true on two counts. First, the interior lines are straight, not ellipsoidal. Second, and more importantly, two magnetic field lines can never intersect. If they did, the compass needle placed at the crossing point would have to point in two different directions at the same time, which is impossible.
So option 1 is the false statement and is the required answer.
❌ Why the other options are incorrect
✗ Uniform inside the solenoid — this is true; that is the very reason solenoids are used to produce uniform fields.
✗ Along the axis and parallel to each other — true; the fields of all the turns add up along the axis.
✗ The same at all points inside the solenoid — true, and it is simply another way of saying the field is uniform.
📌 SSC & Railway Exam Facts
• Magnetic field lines never intersect — a basic property of field lines.
• Field inside a solenoid: B = μ₀nI, where n = turns per unit length.
• Field lines come out of the north pole and go into the south pole outside a magnet.
• A solenoid behaves like a bar magnet; with a soft iron core it becomes an electromagnet.
• Closer field lines mean a stronger magnetic field.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 1 · Solenoid and electromagnet

Q92. A soft iron bar is introduced inside the current carrying solenoid. What is the magnetic field inside a current-carrying solenoid when a bar made of soft iron is introduced inside the solenoid?

  1. (a) Will remain same
  2. (b) Will become zero
  3. (c) Will decrease
  4. (d) Will increase
Answer & solution

Answer: (d) Will increase

Correct Answer: Option 4 — Will increase
When a soft iron bar is placed inside a current-carrying solenoid, the magnetic field inside the coil increases greatly, and the arrangement becomes an electromagnet.
Soft iron is a ferromagnetic material. The field of the solenoid lines up the tiny magnetic domains inside the iron, so the iron itself becomes strongly magnetised and adds its own field to that of the solenoid. Since the relative permeability of soft iron is several hundred to a few thousand times that of air, the resultant field becomes hundreds of times stronger.
In formula terms the field changes from B = μ₀nI (air core) to B = μ₀μ(r)nI (iron core), where μ(r) ≫ 1.
Soft iron is chosen as the core because it is magnetised strongly but loses its magnetism as soon as the current is switched off — exactly what a controllable electromagnet needs.
❌ Why the other options are incorrect
✗ Will remain same — this would be true only for a non-magnetic core such as wood, plastic or copper.
✗ Will become zero — nothing can cancel the field of the current; the current keeps flowing and so the field remains.
✗ Will decrease — the field would weaken only for a diamagnetic material, and even then the change is extremely small; soft iron does the opposite.
📌 SSC & Railway Exam Facts
• Field inside a solenoid with a core: B = μ₀μ(r)nI.
• Soft iron is used for electromagnet cores (temporary magnets); steel is used for permanent magnets.
• Electromagnets are used in electric bells, cranes lifting scrap iron, loudspeakers, relays and MRI machines.
• Hans Christian Oersted (1820) discovered the magnetic effect of current; William Sturgeon made the first electromagnet.
• The strength of an electromagnet increases with the current, the number of turns and a soft iron core.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 2 · Solenoid and electromagnet

Q93. Which of the following statements is/are correct?
Statements:
I) A current carrying coil produces magnetic field.
II) A current carrying solenoid behaves like a bar magnet.

  1. (a) Statement I only
  2. (b) Statement II only
  3. (c) Both Statements I and II
  4. (d) Neither Statement I nor II
Answer & solution

Answer: (c) Both Statements I and II

Correct Answer: Option 3 — Both Statements I and II
Statement I is correct. Every current-carrying conductor produces a magnetic field around it — this is the magnetic effect of electric current, discovered by Hans Christian Oersted in 1820. In a circular coil the field lines are circles near the wire, and at the centre of the coil they become nearly straight and perpendicular to the plane of the coil. With n turns, the field at the centre becomes n times that of a single turn.
Statement II is also correct. A solenoid is a long cylindrical coil of many closely wound turns. When current flows, the field inside is strong and uniform, and the pattern outside is exactly like that of a bar magnet — one face acts as the north pole and the other as the south pole. Placing a soft iron core inside turns it into a powerful electromagnet.
Since both statements are true, the correct option is Both Statements I and II.
❌ Why the other options are incorrect
✗ Statement I only — it wrongly rejects Statement II, but a solenoid genuinely behaves like a bar magnet.
✗ Statement II only — it wrongly rejects Statement I, yet a current-carrying coil certainly produces a magnetic field.
✗ Neither Statement I nor II — both statements are standard NCERT facts, so rejecting both is wrong.
📌 SSC & Railway Exam Facts
• Field inside a solenoid: B = μ₀nI, where n is turns per unit length.
• Direction of the field is found by the right-hand thumb rule; for a coil use the clock rule.
• SI unit of magnetic field is the tesla (T); 1 T = 1 N/(A m).
• Electromagnets use soft iron; permanent magnets use steel or alnico.
• Fleming's left-hand rule → electric motor; Fleming's right-hand rule → generator.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 2 · Magnetic field due to current (Oersted, right-hand thumb rule)

Q94. If the magnetic field due to a single turn circular coil is B. Then the value of magnetic field due a circular coil with 10 turns will be: (Other parameters are to be kept same)

  1. (a) 100B
  2. (b) B
  3. (c) 10B
  4. (d) 5B
Answer & solution

Answer: (c) 10B

Correct Answer: Option 3 — 10B
📖 Given
• Magnetic field at the centre of a single turn coil = B
• Number of turns in the new coil, n = 10
• Current I and radius r are kept the same
✍️ Formula
B = μ₀nI/2r — the field at the centre of a circular coil of n turns
🔢 Solution
• For one turn (n = 1): B = μ₀I/2r
• For ten turns (n = 10): B′ = μ₀ × 10 × I/2r
• B′ = 10 × (μ₀I/2r)
• B′ = 10B
Each turn carries the same current in the same direction, so the fields of all ten turns simply add up at the centre, making the field ten times stronger.
❌ Why the other options are incorrect
✗ 100B — this comes from wrongly squaring the number of turns; the field is proportional to n, not to n².
✗ B — the field would stay B only if the extra turns produced nothing, but every extra turn adds its own field.
✗ 5B — this is half the correct value, obtained by wrongly taking only 5 of the 10 turns into account.
📌 SSC & Railway Exam Facts
• Field at centre of a circular coil: B = μ₀nI/2r — proportional to n and I, inversely proportional to r.
• Field inside a long solenoid: B = μ₀nI, where n is turns per unit length.
• μ₀ = 4π × 10⁻⁷ T m/A is the permeability of free space.
• Direction of the field is given by the right-hand thumb rule.
• Oersted (1820) discovered that a current-carrying wire deflects a magnetic compass needle.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 3 · Magnetic field and field lines

Q95. Which statement is NOT true for magnetic field lines?

  1. (a) Magnetic field lines are not closed curves.
  2. (b) Inside the magnet, the direction of field lines is from its south pole to its north pole.
  3. (c) No two field lines are found to cross each other.
  4. (d) The relative strength of the magnetic field is shown by the degree of closeness of the field lines.
Answer & solution

Answer: (a) Magnetic field lines are not closed curves.

Correct Answer: Option 1 — Magnetic field lines are not closed curves.
This statement is false. Magnetic field lines are always closed, continuous curves. Outside a magnet they run from the north pole to the south pole, and inside the magnet they continue from the south pole back to the north pole, closing the loop.
This happens because isolated magnetic poles (monopoles) do not exist — a magnet always has both poles together, so the lines can never simply begin or end somewhere in space. Electric field lines, by contrast, do start on positive charges and end on negative charges, and are therefore not closed.
Since the question asks which statement is NOT true, the answer is this first option.
❌ Why the other options are incorrect
✗ Inside the magnet, the direction of field lines is from its south pole to its north pole. — this is true; it is exactly what makes the lines closed loops.
✗ No two field lines are found to cross each other. — true; if they crossed, the compass needle would show two directions of the field at one point, which is impossible.
✗ The relative strength of the magnetic field is shown by the degree of closeness of the field lines. — true; crowded lines mean a stronger field, and the lines are closest near the poles.
📌 SSC & Railway Exam Facts
• Magnetic field lines are closed curves: N → S outside, S → N inside the magnet.
• SI unit of magnetic field is the tesla (T); the CGS unit is the gauss; 1 T = 10⁴ gauss.
• Field lines are drawn with a compass needle or with iron filings sprinkled around a magnet.
• Magnetic monopoles do not exist — breaking a magnet gives two smaller magnets, each with both poles.
• Oersted (1820) showed that a current-carrying wire deflects a compass needle.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 1 · Solenoid and electromagnet

Q96. What is the strength of the magnetic field found inside a current carrying solenoid?

  1. (a) Same at all points
  2. (b) Minimum in the middle
  3. (c) Found to increase from one end to the other
  4. (d) More at the ends than at the centre
Answer & solution

Answer: (a) Same at all points

Correct Answer: Option 1 — Same at all points
A solenoid is a long coil of many closely wound circular turns of insulated copper wire. When a current flows, the magnetic fields of the neighbouring turns add up along the axis and cancel sideways, so that inside the solenoid the field lines come out straight, parallel and equally spaced.
Parallel, equally spaced field lines are the signature of a uniform magnetic field — a field having the same magnitude and the same direction at every point. Hence the field strength inside a long current-carrying solenoid is the same at all points. Its value is B = μ₀nI, where n is the number of turns per unit length; note that it does not depend on the position inside or on the radius of the coil. Placing a soft iron core inside makes a powerful electromagnet.
❌ Why the other options are incorrect
✗ Minimum in the middle — exactly wrong; the middle region is where the field is most perfectly uniform and strong. The field weakens only near and beyond the ends.
✗ Found to increase from one end to the other — this would mean the field lines get steadily closer together, which is not the pattern seen inside a solenoid.
✗ More at the ends than at the centre — the opposite is true; at the very ends the field falls to about half its central value because the lines begin to spread out.
📌 SSC & Railway Exam Facts
• Field inside a long solenoid: B = μ₀nI, uniform; outside, the pattern resembles a bar magnet.
• μ₀ = 4π × 10⁻⁷ T m A⁻¹ (permeability of free space); SI unit of B is the tesla (T).
• Uniform field ⇒ parallel, equidistant field lines; crowded lines ⇒ stronger field.
• A soft iron core turns a solenoid into an electromagnet; William Sturgeon made the first one in 1824.
• Right-hand thumb rule — thumb → current, curled fingers → magnetic field.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 2 · Solenoid and electromagnet

Q97. The magnetic field lines inside a current carrying solenoid are in the form of:

  1. (a) parallel straight lines
  2. (b) curved lines
  3. (c) perpendicular straight lines
  4. (d) concentric circles
Answer & solution

Answer: (a) parallel straight lines

Correct Answer: Option 1 — parallel straight lines
A solenoid is a long coil of many circular turns of insulated copper wire wound closely in the shape of a cylinder. When current flows, the magnetic field produced by every single turn adds up inside the coil.
Inside the solenoid the magnetic field lines come out as parallel straight lines, all pointing in the same direction along the axis. This means the field inside a solenoid is uniform — it has the same magnitude and direction at every point of that region.
Outside, the pattern is exactly like that of a bar magnet — one end behaves as the north pole and the other as the south pole.
❌ Why the other options are incorrect
✗ curved lines — the lines curve only outside the solenoid, where they spread from one end round to the other.
✗ perpendicular straight lines — the lines run along the axis of the solenoid, never at right angles to it.
✗ concentric circles — that is the pattern of the field around a straight current-carrying wire, not inside a solenoid.
📌 SSC & Railway Exam Facts
• Field inside a solenoid: B = μ₀nI, where n is the number of turns per unit length.
• Putting a soft iron core inside a solenoid makes a powerful electromagnet.
• The direction of the field is found by the right-hand thumb rule (Maxwell's corkscrew rule).
• The SI unit of magnetic field is the tesla (T).
• Hans Christian Oersted (1820) discovered the magnetic effect of electric current.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 3 · Solenoid and electromagnet

Q98. What is the nature of the magnetic field inside a current-carrying solenoid?

  1. (a) Strong non-uniform magnetic field
  2. (b) Weak uniform magnetic field
  3. (c) Strong uniform magnetic field
  4. (d) Weak non-uniform magnetic field
Answer & solution

Answer: (c) Strong uniform magnetic field

Correct Answer: Option 3 — Strong uniform magnetic field
A solenoid is a long cylindrical coil made of many closely wound circular turns of insulated copper wire. When a current flows, each turn produces its own magnetic field and all these fields add up along the axis.
Inside the solenoid the field lines are parallel straight lines of the same direction and the same closeness everywhere. Equally spaced parallel lines mean the field has the same magnitude and same direction at every point — that is, it is uniform. Because the contributions of hundreds of turns add together, the field is also strong.
Its strength is B = μ₀nI, where n is the number of turns per unit length. Outside, the solenoid behaves exactly like a bar magnet, with one end acting as the north pole and the other as the south pole.
❌ Why the other options are incorrect
✗ Strong non-uniform magnetic field — the field is strong, but inside a solenoid it is not non-uniform; non-uniform fields occur near the ends and outside.
✗ Weak uniform magnetic field — uniform is right, but the many turns make the field strong, not weak.
✗ Weak non-uniform magnetic field — both parts are wrong for the region inside the solenoid.
📌 SSC & Railway Exam Facts
• Field inside a solenoid: B = μ₀nI; SI unit of magnetic field is the tesla (T).
• Placing a soft iron core inside a solenoid makes a strong electromagnet.
• Direction of the field is given by the right-hand thumb rule.
• Hans Christian Oersted (1820) discovered the magnetic effect of electric current.
• Around a straight current-carrying wire, field lines are concentric circles.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 1 · Magnetic field and field lines

Q99. Inside a bar magnet, the direction of magnetic field lines is from its:

  1. (a) South pole to its North pole
  2. (b) always perpendicular to the South pole
  3. (c) always perpendicular to the North pole
  4. (d) North pole to its South pole
Answer & solution

Answer: (a) South pole to its North pole

Correct Answer: Option 1 — South pole to its North pole
Magnetic field lines always form closed continuous loops. Outside a bar magnet they run from the North pole to the South pole, but the loop must be completed, so inside the magnet they run from the South pole to the North pole. This is exactly what makes them different from electric field lines, which start and end on charges.
Other important properties: field lines never intersect one another (if they did, the compass needle would have two directions at one point); they are crowded where the field is strong (near the poles) and far apart where it is weak; and the tangent at any point gives the direction of the magnetic field there.
❌ Why the other options are incorrect
✗ North pole to its South pole — that is the direction of the field lines outside the magnet, in the surrounding space, not inside its body.
✗ always perpendicular to the South pole — field lines leave or enter the pole faces but they do not stay perpendicular; inside the magnet they run along its length.
✗ always perpendicular to the North pole — same mistake; the lines inside a bar magnet are directed along the magnet, from S to N, forming closed loops.
📌 SSC & Railway Exam Facts
• Magnetic field lines are closed curves: N → S outside the magnet and S → N inside it.
• Field lines never cross; the tangent at a point gives the field direction; their crowding shows the field strength.
• SI unit of magnetic field (B) is tesla (T); of magnetic flux it is weber (Wb); 1 T = 1 Wb/m².
• Like poles repel, unlike poles attract; a freely suspended magnet points north–south.
• The magnetic effect of electric current was discovered by Hans Christian Oersted in 1820.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 2 · Magnetic field and field lines

Q100. Considering magnetic field lines, which of the following statements is NOT true?

  1. (a) If magnetic field lines are parallel and equidistant, they represent zero field strength.
  2. (b) The direction of the magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points.
  3. (c) The relative strength of magnetic field exists and can be shown by the degree of closeness of the field lines.
  4. (d) Magnetic field lines are closed curves.
Answer & solution

Answer: (a) If magnetic field lines are parallel and equidistant, they represent zero field strength.

Correct Answer: Option 1 — If magnetic field lines are parallel and equidistant, they represent zero field strength.
This statement is false, so it is the answer to a "NOT true" question. Parallel and equally spaced field lines represent a uniform magnetic field — a field that has the same magnitude and same direction at every point, not a zero field. The field inside a long current-carrying solenoid and the field in a small region between the poles of a horseshoe magnet are of this kind.
A zero field would be shown by no field lines at all in that region, for example at the neutral point where the field of a bar magnet exactly cancels the Earth's field.
❌ Why the other options are incorrect
✗ The direction of the magnetic field ... north pole of a magnetic compass needle points. — true; this is the standard definition of field direction, and it is why field lines run N → S outside a magnet.
✗ The relative strength ... degree of closeness of the field lines. — true; crowded lines mean a stronger field, which is why lines bunch up near the poles.
✗ Magnetic field lines are closed curves. — true; a line goes from N to S outside the magnet and continues from S to N inside it, forming a closed loop.
📌 SSC & Railway Exam Facts
• Two magnetic field lines never intersect, otherwise the compass would point in two directions at once.
• SI unit of magnetic field B is the tesla (T); 1 T = 10⁴ gauss.
• Magnetic field lines are closed because isolated magnetic poles (monopoles) do not exist.
• Field due to a straight current-carrying wire is given by the right-hand thumb rule; force on a conductor by Fleming's left-hand rule.
12

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