Physics Miscellaneous PYQs – Physics, SSC & Railway

Answer: Option 1 — Barometer
A barometer measures atmospheric pressure — the weight of the column of air above a place.
A thermometer measures temperature, an ammeter electric current and a hygrometer humidity.
Revision note — Atmospheric pressure and the barometer
• The mercury barometer was invented by Evangelista Torricelli in 1643; at sea level the air supports a mercury column of 76 cm (760 mm).
• 1 atmosphere = 760 mm of Hg = 1.013 × 10⁵ Pa = 1,013 millibar (hPa); the SI unit of pressure is the pascal.
• An aneroid barometer uses a sealed, partly evacuated metal box instead of mercury; a barograph records pressure continuously on a chart.
• Pressure falls with height — that is why an altimeter in an aircraft is really a barometer.
• A sudden fall in the barometer warns of a storm; a slow rise means fair, dry weather.
• Weather instruments to remember: anemometer — wind speed; wind vane — wind direction; hygrometer — humidity; rain gauge — rainfall; thermometer — temperature.
Do not mix these up
• Barometer vs manometer — a barometer measures the pressure of the atmosphere; a manometer measures the pressure of a gas in a container against it.
• Hygrometer vs hydrometer — a hygrometer measures the moisture of air; a hydrometer measures the density of a liquid.
Also asked from this topic: the instruments for wind speed, humidity and pressure (anemometer, hygrometer, barometer); why we are not crushed by the atmosphere (the pressure inside the body balances it).

Answer: Option 3 — Radio Telescope
The cosmic microwave background peaks in the microwave band, at a wavelength of about 1.9 mm, and the microwave band lies inside the radio region of the electromagnetic spectrum.
Only a radio (microwave) telescope, with its large parabolic dish, can collect it.
Revision note — Cosmic microwave background and telescopes
• The CMB is the relic radiation left from about 380,000 years after the Big Bang, when the universe first became transparent; its temperature today is 2.725 K.
• It was found by accident in 1965 by Arno Penzias and Robert Wilson at Bell Laboratories; they shared the Nobel Prize in Physics in 1978.
• Satellites that mapped it: COBE (1989), WMAP (2001) and the ESA's Planck (2009).
• A radio telescope collects radio waves with a large dish-shaped parabolic antenna.
• India's biggest is the Giant Metrewave Radio Telescope (GMRT) at Khodad near Pune, with 30 dishes of 45 m; India is also a member of the Square Kilometre Array.
• The Event Horizon Telescope, a worldwide network of radio telescopes, produced the first direct image of a black hole (M87*) on 10 April 2019.
• X-ray and gamma-ray telescopes must be in space — Chandra, India's AstroSat (2015) and XPoSat (2024) — because the atmosphere absorbs those rays.
• Radio waves and visible light pass through atmospheric windows, which is why radio and optical telescopes work from the ground.
Do not mix these up
• Radio vs infrared telescope — infrared instruments such as the James Webb Space Telescope see dust-shrouded stars by their heat; the CMB is far longer in wavelength and needs a microwave dish.
• Microwave vs radio — microwaves are not a separate spectrum; they are the short-wavelength end of the radio band.
Also asked from this topic: the telescope used to observe radio waves from space (radio telescope); the telescope that gave the first image of a black hole (Event Horizon Telescope).

Answer: Option 3 — MACE uses space-based sensors to directly detect cosmic gamma rays without atmospheric distortion.
MACE is a ground-based telescope; it never sees the gamma ray itself.
It records the faint blue Cherenkov flash that the gamma ray's air shower produces in the atmosphere — so the atmosphere is its detector, not a nuisance.
Revision note — MACE telescope, Hanle
• Major Atmospheric Cherenkov Experiment (MACE) was inaugurated on 4 October 2024 at Hanle, Ladakh, during the Platinum Jubilee of the Department of Atomic Energy.
• Built by BARC (Bhabha Atomic Research Centre) with ECIL and other Indian industry partners — an indigenous project.
• Site altitude about 4,300 m, making MACE the highest imaging Cherenkov telescope in the world and the largest in Asia.
• Dish diameter 21 m, weight about 180 tonnes, with a camera of 1,088 photomultiplier pixels; it works in the very high energy gamma-ray band (tens of GeV to TeV).
• Targets: supernova remnants, pulsars, active galactic nuclei, gamma-ray bursts and searches for dark matter signals.
• Hanle also hosts the Indian Astronomical Observatory of the Indian Institute of Astrophysics (Himalayan Chandra Telescope, 2 m) and became India's first Dark Sky Reserve in 2022.
• The earlier Indian gamma-ray facilities were HAGAR at Hanle and TACTIC at Mount Abu.
Do not mix these up
• MACE vs AstroSat — MACE is a ground-based Cherenkov telescope; AstroSat (2015) is India's space observatory that detects X-rays and ultraviolet directly from orbit.
• Cherenkov telescope vs optical telescope — an optical telescope collects the object's own light; a Cherenkov telescope collects a secondary flash made in the air by a gamma ray that never reaches the ground.
Also asked from this topic: where MACE was inaugurated (Hanle, 4 October 2024); Ladakh's high-altitude observatory (IAO, Hanle); why solar gamma rays never reach the ground (absorbed high up).

Answer: Option 3 — MACE detects very high-energy gamma rays indirectly by capturing Cherenkov radiation produced in the Earth's atmosphere, unlike optical telescopes which observe direct light from celestial sources.
Gamma rays are absorbed high in the atmosphere, so no ground telescope can see them directly.
MACE instead images the nanosecond blue Cherenkov flash from the shower of particles the gamma ray creates — an indirect, ground-based method; an optical telescope simply gathers the star's own light.
Revision note — Cherenkov radiation and gamma-ray astronomy
• Cherenkov radiation is the faint blue light emitted when a charged particle moves through a medium faster than light travels in that medium (never faster than light in vacuum).
• Discovered by Pavel Cherenkov in 1934; he shared the 1958 Nobel Prize in Physics with Ilya Frank and Igor Tamm, who explained it. It is also the blue glow seen in the water of a nuclear reactor.
• A very high-energy gamma ray hitting the upper atmosphere produces an extensive air shower of electrons and positrons.
• Those particles emit a Cherenkov flash lasting a few nanoseconds that lights up a patch of ground about 250 m across.
• An Imaging Atmospheric Cherenkov Telescope (IACT) such as MACE uses a large mirror and a fast photomultiplier camera to photograph that flash and work back to the gamma ray's direction and energy.
• MACE (21 m dish, Hanle, Ladakh, inaugurated 4 October 2024, built by BARC) is Asia's largest and the world's highest IACT.
• The other big Cherenkov arrays are HESS (Namibia), MAGIC (La Palma) and VERITAS (Arizona).
• Gamma rays of lower energy are studied from space — NASA's Fermi telescope, and India's AstroSat (2015) in the X-ray and ultraviolet bands.
• Gamma-ray sources: pulsars, supernova remnants, active galactic nuclei (blazars) and gamma-ray bursts — the most energetic explosions known.
Do not mix these up
• Cherenkov radiation vs the speed-of-light limit — the particle beats light in air or water, where light is slowed; nothing exceeds light's speed in vacuum.
• Ground-based Cherenkov telescope vs space gamma-ray telescope — the ground telescope catches a secondary flash in air; the space telescope catches the gamma ray itself above the atmosphere.
Also asked from this topic: where MACE was inaugurated (Hanle, 4 October 2024); why solar gamma rays do not reach the ground (absorbed high in the atmosphere).

Concept: History of Solar Radiation Measurement in India
Anna Mani, an eminent Indian physicist and meteorologist, led pioneering work in standardizing meteorological instruments in India and carried out systematic solar radiation (insolation) measurements across the country. Her work produced the foundational solar radiation data/atlas that later informed India's solar energy potential mapping — this is a well-established historical/GK fact frequently referenced in the context of India's renewable energy planning.
Correct Answer: Anna Mani's solar radiation measurements

Answer: Option 2 – Electron Beam.
• A light microscope uses visible light; anelectron microscope uses an electron beam.

Answer: Option 3 – Blood pressure.
• Asphygmomanometermeasuresblood pressure.

Correct Answer: Isaac Newton (Option 1)
Sir Isaac Newton was the first to explain the dispersion of white light into a spectrum of colours (VIBGYOR) in 1666. He passed sunlight through a glass prism and demonstrated that white light is composed of seven colours — Violet, Indigo, Blue, Green, Yellow, Orange, and Red. He also used a second prism to recombine the spectrum back into white light, proving that dispersion is a property of light.
Why others are wrong:
- Thomas Young: Known for the double-slit experiment demonstrating the wave nature of light (1801); not the discoverer of dispersion.
- Huygens: Proposed the wave theory of light; did not explain dispersion.
- Maxwell: Formulated the electromagnetic theory of light; unrelated to prism dispersion.

Correct Answer: Radio telescope — Option (c)
A radio telescope is used to detect and study radio waves emitted by celestial objects in space. Unlike optical telescopes that collect visible light, radio telescopes use large dish-shaped antennas (parabolic reflectors) to collect radio waves, which are then amplified and analyzed. Famous radio telescopes include the Arecibo Observatory (Puerto Rico, now decommissioned), the Very Large Array (VLA) in New Mexico, and India's GMRT (Giant Metrewave Radio Telescope) near Pune. Radio astronomy has led to discoveries of pulsars, quasars, and the cosmic microwave background radiation.
Option (a) Optical telescope — Incorrect: Optical telescopes detect visible light; they cannot observe radio waves from space.
Option (b) Reflecting telescope — Incorrect: A reflecting telescope uses mirrors to collect visible light; it is a type of optical telescope, not designed for radio waves.
Option (d) Refracting telescope — Incorrect: A refracting telescope uses lenses to bend visible light; it cannot detect radio waves from space.

Correct Answer: 0.009 radian — Option (a)
Angular diameter (in radians) = Diameter of object / Distance to object
Angular diameter = 3,474 km / 384,000 km = 0.00904... ≈ 0.009 radian
This formula applies when the angle is small (small angle approximation), which is valid here since the Moon subtends a very small angle (about 0.5°) as seen from Earth. The angular diameter of 0.009 radians is consistent with the Moon appearing about 0.5° in the sky (0.009 rad × 180/π ≈ 0.52°).
Option (b) 0.008 radian — Incorrect: 0.008 radian would require a distance of 3474/0.008 = 434,250 km, which is not the average Earth-Moon distance.
Option (c) 0.010 radian — Incorrect: 0.010 radian would require a distance of 3474/0.010 = 347,400 km, which is less than the average Earth-Moon distance.
Option (d) 0.007 radian — Incorrect: 0.007 radian would require a distance of 3474/0.007 = 496,286 km, which is beyond the typical lunar distance.

Topic: Law of Inertia (Newton's First Law)
Galileo Galilei conducted experiments with inclined planes and rolling balls in the early 1600s.
He observed that objects in motion tend to stay in motion unless acted upon by external forces.
His experiments laid the foundation for Newton's First Law of Motion (Law of Inertia).
Answer: Option 4 → Galileo Galilei

Correct Answer: Benjamin Franklin (Option 2)
Benjamin Franklin (1706–1790) conducted his famous kite experiment in 1752, in which he flew a kite during a thunderstorm and demonstrated that lightning is an electrical phenomenon — essentially the same as the sparks produced by rubbing clothes (static electricity). This discovery led to the invention of the lightning rod.
Why other options are wrong:
Option 1 – Isaac Newton is known for laws of motion, universal gravitation, and calculus.
Option 3 – William Nicholson was a British chemist known for the electrolysis of water.
Option 4 – Thomas Edison is known for inventing the phonograph and practical incandescent light bulb.

Correct Answer: Both I and II (Option 3)
Lightning can strike both telephone cords and electrical wires. Both are conductive and can act as pathways for electrical discharge during a lightning strike. Telephone lines and electrical wires connected to poles or buildings can transmit the electrical energy from a lightning bolt into a building, causing damage or injury.
This is why it is advised to avoid using corded telephones and to unplug electrical appliances during thunderstorms.
Since both Statement I and Statement II are correct, the answer is Both I and II.

A Hydrometer is an instrument used to measure the specific gravity (relative density) of liquids. It works on the principle of Archimedes and floats at different levels depending on the density of the liquid.
Why other options are incorrect:
- Lactometer: A specific type of hydrometer used only to test the purity of milk, not liquids in general.
- Ammeter: Used to measure electric current in a circuit; not related to density.
- Barometer: Used to measure atmospheric pressure; has no role in measuring liquid density.

A Sphygmomanometer is the instrument used to measure blood pressure. It measures systolic and diastolic pressure and is expressed in millimetres of mercury (mmHg). Normal blood pressure is approximately 120/80 mmHg.
Why other options are incorrect:
- Hygrometer: Measures atmospheric humidity, not blood pressure.
- Thermometer: Measures body or environmental temperature.
- Weighing balance: Measures the mass of objects; has no role in measuring blood pressure.

Correct Answer: 3 – Isaac Newton.
Sir Isaac Newton formulated the Universal Law of Gravitation, which states that every object in the universe attracts every other object with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them. The famous story of Newton observing a falling apple inspired him to extend this concept to the Moon and all objects in the universe.
Albert Einstein (Option 1) developed the Theory of Relativity and General Relativity, which extended Newton's concept of gravity.
Thomas Edison (Option 2) was an inventor known for the electric bulb and phonograph, not gravitation.
Galileo Galilei (Option 4) made discoveries about motion and falling bodies, but did not formulate the universal law of gravitation.

Correct Answer: 1 – Coiled spring .
A spring balance (spring scale) works on the principle of Hooke's Law. Inside the spring balance is a coiled spring that stretches (elongates) proportionally when a force (load) is applied. The amount of stretching corresponds to the magnitude of the applied force, which is indicated on the scale.
A clock (Option 2), metal rod (Option 3), and lever (Option 4) are not components of a spring balance.

The correct answer is (a) Meghnad Saha.
Meghnad Saha (1893-1956), the eminent astrophysicist known for his Thermal Ionization Equation (Saha Ionization Equation), chaired the Indian Calendar Reform Committee (1952-1955). The committee proposed the National Calendar of India (Saka Calendar), adopted in 1957, which standardized the many regional calendars in India and aligned them with the Gregorian calendar.
(b) Vikram Sarabhai: Father of India's space program; established ISRO; not associated with the Calendar Reform Committee.
(c) P.C. Mahalanobis : Renowned statistician; founder of the Indian Statistical Institute; known for the Mahalanobis distance; not associated with calendar reform.
(d) C.V. Raman: Nobel laureate (1930) for discovery of the Raman Effect; worked in optics and spectroscopy; not associated with the Calendar Reform Committee.

The Eddy Covariance (EC) tower installed by ISRO at RPCAU, Bihar is used to continuously measure the exchange of CO2, water vapour , and energy fluxes between the land surface (agricultural ecosystem) and the atmosphere. This data helps understand carbon sequestration, evapotranspiration, and the climate impact on agriculture.
(a) Incorrect: Sounding rockets are launched from dedicated ISRO facilities, not agricultural universities.
(c) Incorrect: Astronaut training is conducted at facilities like the Astronaut Training Centre, not RPCAU.
(d) Incorrect: Providing Wi-Fi is not the function of an Eddy Covariance tower.

The correct answer is Albert Einstein (Option 2).
Albert Einstein developed the General Theory of Relativity, published in 1915. It fundamentally changed our understanding of gravity, space, and time, describing gravity as the curvature of spacetime caused by mass and energy.
Option 1 - Werner Heisenberg: Developed the Uncertainty Principle and made foundational contributions to quantum mechanics, not the General Theory of Relativity.
Option 3 - Niels Bohr: Developed the atomic model and contributed to quantum mechanics; not associated with the General Theory of Relativity.
Option 4 - Max Planck: Developed quantum theory (Planck's constant); not associated with the General Theory of Relativity.

Correct Answer: Option 2 – Pressure
A barometer is a scientific instrument used to measure atmospheric (air) pressure. The mercury barometer was invented by Evangelista Torricelli in 1643. The aneroid barometer (portable, no liquid) is also widely used. Barometric pressure readings are fundamental to weather forecasting — falling pressure indicates approaching storms; rising pressure indicates fair weather.
Option 1 (Distance): Distance is measured by odometers, rangefinders, or rulers — not barometers.
Option 3 (Speed): Speed is measured by speedometers, anemometers (wind speed), or tachometers — not barometers.
Option 4 (Temperature): Temperature is measured by thermometers — not barometers.

Correct Answer: Option 3 – 1-Anemometer, 2-Hygrometer, 3-Barometer
Wind Speed → Anemometer: Measures wind speed (and sometimes direction). The cup anemometer (rotating cups) is most common; rotation rate gives wind speed in km/h or m/s.
Humidity → Hygrometer: Measures atmospheric water vapour content (relative humidity). Types include wet-and-dry-bulb (psychrometer), hair hygrometer, and electronic humidity sensors.
Atmospheric Pressure → Barometer: Measures atmospheric (air) pressure. Mercury barometer (Torricelli) and aneroid barometer are the two main types; used in weather forecasting.
Option 1 (Hygrometer-Barometer-Anemometer): All three instruments are assigned to wrong phenomena.
Option 2 (Barometer-Anemometer-Hygrometer): Incorrect — wind speed and humidity instruments are swapped.
Option 4 (Hygrometer-Anemometer-Barometer): Only atmospheric pressure (3-Barometer) is correct; wind speed and humidity are swapped.

Correct Answer: Option 3 – 1-Anemometer, 2-Hygrometer, 3-Barometer
Wind Speed → Anemometer: An anemometer measures wind speed (and sometimes direction). The cup anemometer (three or four cups rotating on a vertical axis) is the most common type; wind speed is calculated from the rotation rate.
Humidity → Hygrometer: A hygrometer measures atmospheric humidity (the amount of water vapour in the air). Types include wet-and-dry-bulb hygrometers (psychrometers), hair hygrometers, and electronic humidity sensors.
Atmospheric Pressure → Barometer: A barometer measures atmospheric (air) pressure. The mercury barometer (Torricelli) and aneroid barometer are the two common types; barometric readings are used in weather forecasting.
Option 1 (Hygrometer-Barometer-Anemometer): Incorrect assignment for all three.
Option 2 (Barometer-Anemometer-Hygrometer): Incorrect — swaps the instruments for wind speed and humidity.
Option 4 (Hygrometer-Anemometer-Barometer): Only atmospheric pressure (3-Barometer) is correct; wind speed and humidity are swapped.

Correct Answer: Option 2 — Faraday
Electromagnetic induction was discovered by the English scientist Michael Faraday in 1831. He showed that when the magnetic field linked with a coil changes, an electric current is set up in the coil. The current so produced is called an induced current and the voltage an induced emf.
Faraday's law states that the induced emf is proportional to the rate of change of magnetic flux through the circuit. The direction of the induced current is given by Fleming's right-hand rule (or Lenz's law). This single discovery is the basis of the electric generator (dynamo), the transformer and the entire power-supply system.
❌ Why the other options are incorrect
✗ Einstein — Albert Einstein gave the theory of relativity and explained the photoelectric effect, for which he received the Nobel Prize in 1921.
✗ Edison — Thomas Alva Edison invented the practical incandescent electric bulb, the phonograph and the motion-picture camera.
✗ Newton — Isaac Newton gave the three laws of motion and the law of universal gravitation, not electromagnetic induction.
📌 SSC & Railway Exam Facts
• Michael Faraday also gave the laws of electrolysis and discovered benzene.
• Lenz's law — the induced current always opposes the change producing it; it follows from the conservation of energy.
• An electric generator converts mechanical energy into electrical energy; an electric motor does the reverse.
• The magnetic effect of current was discovered by Hans Christian Oersted in 1820.
• SI unit of magnetic flux is weber (Wb) and of magnetic field is tesla (T).

Correct Answer: Option 3 — Isaac Newton
Sir Isaac Newton, in 1666, was the first to pass a narrow beam of sunlight through a glass prism and obtain a band of seven colours on a screen. He named this band the spectrum. The splitting of white light into its constituent colours is called dispersion.
The seven colours in order are VIBGYOR — Violet, Indigo, Blue, Green, Yellow, Orange, Red. Dispersion happens because the refractive index of glass is different for different colours: violet has the shortest wavelength and bends the most, while red has the longest wavelength and bends the least.
Newton went further and showed that the spectrum could be recombined into white light by placing a second, inverted prism next to the first — proving that the colours were present in sunlight itself and not created by the prism.
❌ Why the other options are incorrect
✗ Einstein — Albert Einstein explained the photoelectric effect and gave the theory of relativity; he did not perform the prism experiment.
✗ Edison — Thomas Alva Edison invented the practical electric bulb and the phonograph; his work was in electricity, not optics.
✗ Fermi — Enrico Fermi built the first nuclear reactor and worked in nuclear physics.
📌 SSC & Railway Exam Facts
• Dispersion = splitting of white light into its seven colours; VIBGYOR is the order from the base of the prism upward.
• Violet deviates most, red deviates least; violet λ ≈ 400 nm, red λ ≈ 700 nm.
• A rainbow is a natural spectrum formed by refraction, total internal reflection and dispersion in water droplets.
• Newton's disc, when spun rapidly, appears white — showing that the seven colours combine into white light.
• Newton also gave the three laws of motion and the law of universal gravitation.

Answer: Option 1 — Michael Faraday
In 1831 Michael Faraday showed that a changing magnetic field through a coil induces a current in it — electromagnetic induction.
Revision note — Electromagnetic induction
• Faraday's law — induced emf is proportional to the rate of change of magnetic flux.
• Lenz's law — the induced current flows so as to oppose the change that produced it.
• Induced current increases with more turns, a stronger magnet and faster motion.
• Fleming's right-hand rule gives the direction of induced current (generator); left-hand rule gives the force on a conductor (motor).
• Applications: AC generator (dynamo), transformer, induction cooktop, metal detector.
• Unit of capacitance, the farad (F), is named after Faraday.
Do not mix these up
• Oersted vs Faraday — Oersted (1820): electric current produces magnetism; Faraday (1831): changing magnetism produces current.
Also asked from this topic: direction of induced current (opposes the change in flux — Lenz's law); principle of generators (electromagnetic induction); a larger induced current (more turns, faster motion).

Answer: Option 3 — Refrigerator
A refrigerator keeps food at a low temperature, which slows the growth of bacteria and fungi, so food stays fresh longer.
A toaster, microwave and electric kettle all heat food or water.
Revision note — How a refrigerator cools
• It pumps heat out of the food compartment and releases it at the back (the black condenser coils) — so the back feels warm.
• The refrigerant absorbs heat as it evaporates inside the cooling pipes — evaporation causes cooling.
• A compressor squeezes the vapour back into liquid so the cycle repeats.
• Older refrigerators used CFCs, which deplete the ozone layer; they are being phased out under the Montreal Protocol (1987).
• Low temperature slows microbial growth and enzyme action — the basis of food preservation by cold storage.
• Appliances like toaster, electric kettle, iron and heater work on the heating effect of current.
Also asked from this topic: a device that earlier used CFCs extensively (refrigerator).