Home › GK Questions Asked › Physics › Human Eye and the Colourful World

Human Eye and the Colourful World PYQs – Physics, SSC & Railway

85 Human Eye and the Colourful World (Physics) questions asked in recent SSC and Railway exams, newest first, with exam, date & shift, answers and solutions.

📚 85 questionsSSC 10 · Railway 75
RRB Group D 2025-26 – 25 August 2026 Shift 1 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q1. A scientist wants to demonstrate why the sky appears blue during the day and reddish at sunset using a glass tank of water, a flashlight, and a small amount of milk. Which setup best demonstrates light scattering similar to that observed in the atmosphere?

  1. (a) Adding a large amount of milk to the water and shining the flashlight through the mixture from above.
  2. (b) Shining the flashlight from above onto clear water and observing the illuminated region.
  3. (c) Shining the flashlight through clear water and observing the transmitted light from the opposite side.
  4. (d) Mixing a small amount of milk into the water and shining the flashlight through the tank from the side to observe scattered light.
Answer & solution

Answer: (d) Mixing a small amount of milk into the water and shining the flashlight through the tank from the side to observe scattered light.

Correct Answer:
Correct Answer: Option 4 – Mixing a small amount of milk into the water and shining the flashlight through the tank from the side to observe scattered light
Explanation:
This setup replicates theTyndall effect, which is analogous to scattering of sunlight by atmospheric particles. A small amount of milk creates fine suspended particles similar in scale to air molecules/dust. Viewing scattered light from theside(perpendicular to the light beam) shows the bluish scattered light (like the sky) while light seen straight through (transmitted) appears reddish (like sunset).
Important Facts:
• Too much milk would scatter almost all light and not properly model the atmosphere.
• Rayleigh scattering explains why shorter (blue) wavelengths scatter more than longer (red) wavelengths.
• This is why the sky is blue during the day and the sun appears reddish at sunrise/sunset.
RRB Group D 2025-26 – 25 August 2026 Shift 2 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q2. A car driver notices that the road ahead appears to be wet during a hot sunny day, but upon reaching the spot, the road is dry. Which physical phenomenon best explains this observation?

  1. (a) Scattering of sunlight by dust particles
  2. (b) Total internal reflection of light within water droplets
  3. (c) Dispersion of sunlight by air molecules
  4. (d) Refraction of light due to varying air temperatures above the road
Answer & solution

Answer: (d) Refraction of light due to varying air temperatures above the road

Correct Answer:
Correct Answer: Option 4 – Refraction of light due to varying air temperatures above the road
Explanation:
This is the classicmiragephenomenon. On a hot day, the air layer just above the road surface is much hotter (and hence less dense/lower refractive index) than the air above it. Light from the sky travelling through these layers of continuously varying density undergoesgradual refraction, bending upward, and eventually appears to reach the observer's eye as if reflected from a 'wet' patch on the road, creating the illusion of water. This is caused by refraction due to the temperature (and density) gradient in air, not scattering or dispersion.
Important Facts:
• Mirage is an example of atmospheric refraction combined with (apparent) total internal reflection at the boundary between hot and cooler air layers.
• It is not due to water droplets since the road is actually dry.
RRB Group D 2025-26 – 25 August 2026 Shift 3 · Power of accommodation, near point and far point

Q3. A student is experiencing difficulty seeing objects clearly both at a distance and up close. After an examination, it is found that the eye muscles are not able to adjust the focal length of the lens properly. Which part of the human eye is most likely responsible for this issue?

  1. (a) Retina
  2. (b) Iris
  3. (c) Cornea
  4. (d) Ciliary muscles
Answer & solution

Answer: (d) Ciliary muscles

Correct Answer:
Correct Answer: Option 4 – Ciliary muscles
Explanation:
The ciliary muscles control the curvature (and hence focal length) of the eye lens, a process called accommodation, allowing the eye to focus on both near and distant objects. If these muscles cannot adjust properly, the person cannot see clearly at both distances — this describes defects like presbyopia.
Important Facts:
• Retina is the light-sensitive screen where the image forms.
• Iris controls the size of the pupil, regulating light entry.
• Cornea is the transparent front part responsible for most of the eye's refraction, but its curvature is fixed, unlike the lens.
RRB Group D 2025-26 – 21 August 2026 Shift 2 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q4. During sunrise or sunset, why does the Sun’s disc appear flattened when observed from Earth?

  1. (a) Because of scattering of sunlight in the atmosphere
  2. (b) Due to gravitational lensing by Earth
  3. (c) Because of absorption of sunlight by air
  4. (d) Due to atmospheric refraction bending light unevenly across the Sun’s disc
Answer & solution

Answer: (d) Due to atmospheric refraction bending light unevenly across the Sun’s disc

Correct Answer:
Correct Answer: Option 4 – Due to atmospheric refraction bending light unevenly across the Sun's disc
Explanation:
Near the horizon, sunlight travels through a much thicker layer of atmosphere. Refraction bends light from the lower edge (limb) of the Sun's disc more than light from the upper edge, since the lower limb's rays pass through denser air at a lower altitude. This unequal bending compresses the vertical dimension of the Sun's disc, making it look flattened (oval) at sunrise and sunset.
Important Facts:
• Atmospheric refraction also makes the Sun visible for a few minutes before actual sunrise and after actual sunset.
• Scattering explains the reddish colour of the Sun near the horizon, not its flattened shape.
RRB Group D 2025-26 – 20 August 2026 Shift 1 · Defects of vision and their correction

Q5. Which of the following defects of vision is corrected using a concave lens?

  1. (a) Hypermetropia
  2. (b) Astigmatism
  3. (c) Presbyopia
  4. (d) Myopia
Answer & solution

Answer: (d) Myopia

Correct Answer:
Correct Answer: Option 4 – Myopia
Explanation:
Myopia(near-sightedness) occurs when the image of a distant object forms in front of the retina. It is corrected using aconcave (diverging) lens, which diverges the incoming rays before they enter the eye, shifting the focal point back onto the retina.
Important Facts:
• Hypermetropia (far-sightedness) is corrected using a convex lens.
• Presbyopia (age-related loss of accommodation) is corrected using bifocal lenses.
• Astigmatism is corrected using a cylindrical lens.
RRB Group D 2025-26 – 20 August 2026 Shift 2 · Prism and dispersion of light

Q6. A student wants to design an experiment to demonstrate the dispersion of white light using a glass prism. Which of the following procedures would best achieve this goal?

  1. (a) Pass white light through a convex lens and look for color changes on a distant wall
  2. (b) Place a triangular glass prism in the path of a narrow white light beam and observe the emerging spectrum on a white screen
  3. (c) Use a concave mirror to reflect the white light onto a wall
  4. (d) Rotate a glass prism randomly in front of a white light source and record any color changes
Answer & solution

Answer: (b) Place a triangular glass prism in the path of a narrow white light beam and observe the emerging spectrum on a white screen

Correct Answer:
Correct Answer: Option 2 – Place a triangular glass prism in the path of a narrow white light beam and observe the emerging spectrum on a white screen.
Explanation:
Dispersion of white light is best demonstrated by passing anarrow beamof white light through a triangular glass prism; the prism splits it into its constituent colours (VIBGYOR) because each colour refracts by a different amount, and this spectrum is observed on a screen.
Important Facts:
• A convex lens or concave mirror does not disperse light into a spectrum in this manner.
• Random rotation of the prism does not constitute a controlled experiment for dispersion.
RRB Group D 2025-26 – 19 August 2026 Shift 1 · Prism and dispersion of light

Q7. Why does the beam of light emerging from a prism show different colours instead of a single white band?

  1. (a) All colours emerge parallel to each other
  2. (b) Some colours get absorbed
  3. (c) Each colour bends at a different angle
  4. (d) All colours bend at the same angle
Answer & solution

Answer: (c) Each colour bends at a different angle

Correct Answer:
Correct Answer: Option 3 – Each colour bends at a different angle
Explanation:
White light is made of several colours (wavelengths). Each colour has adifferent refractive indexin glass, so each colourbends (refracts) by a different anglewhen passing through a prism. This causes the colours to spread out (disperse) into a spectrum (VIBGYOR) instead of exiting as a single white band.
Important Facts:
• This phenomenon is called dispersion of light.
• Violet bends the most and red the least, since violet has the shortest wavelength and highest refractive index.
• A rainbow forms due to dispersion, refraction, and internal reflection of sunlight in water droplets.
RRB Group D 2025-26 – 19 August 2026 Shift 2 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q8. Why do stars appear to twinkle when observed from the Earth?

  1. (a) Due to scattering of light by dust particles in the air
  2. (b) Due to refraction caused by varying air layers in the atmosphere
  3. (c) Due to absorption of light by atmospheric gases
  4. (d) Due to reflection of light from clouds
Answer & solution

Answer: (b) Due to refraction caused by varying air layers in the atmosphere

Correct Answer:
Correct Answer: Option 2 – Due to refraction caused by varying air layers in the atmosphere
Explanation:
Starlight passes through the Earth's atmosphere, which has layers of air at different temperatures and densities. As light continuously refracts (bends) while passing through these changing layers, the apparent position and brightness of the star fluctuates rapidly, causing thetwinklingeffect (atmospheric scintillation).
Important Facts:
• Planets do not twinkle noticeably because they are much closer and appear as extended sources, averaging out the refraction effects.
• This phenomenon is called stellar scintillation.
RRB Group D 2025-26 – 19 August 2026 Shift 3 · Power of accommodation, near point and far point

Q9. When a ciliary muscles contracts, the eye lens becomes __________.

  1. (a) Thinner and the focal length increases
  2. (b) Thicker and the focal length increases
  3. (c) Thicker and the focal length decreases
  4. (d) Thinner and the focal length decreases
Answer & solution

Answer: (c) Thicker and the focal length decreases

Correct Answer:
Option 3 – Thicker and the focal length decreases
Explanation:
When the ciliary musclescontract, they relax the tension on the suspensory ligaments, allowing the eye lens to become more curved (thicker). A more curved (thicker) lens has a shorter focal length, which helps in focusing on nearby objects (accommodation for near vision).
Important Facts:
• When ciliary muscles relax, the lens becomes thinner/flatter, increasing focal length — used for distant vision.
• This adjusting ability of the eye lens is called 'accommodation'.
Correct Answer: Option 3 – Thicker and the focal length decreases
RRB Group D 2025-26 – 18 August 2026 Shift 3 · Defects of vision and their correction

Q10. With ageing, the power of accommodation of the human eye decreases, causing difficulty in viewing nearby objects clearly. This defect is known as:

  1. (a) Myopia
  2. (b) Presbyopia
  3. (c) Hypermetropia
  4. (d) Astigmatism
Answer & solution

Answer: (b) Presbyopia

Concept: Eye Defects
The eye's power of accommodation (its ability to change focal length via the ciliary muscles) naturally declines with age. This age-related loss of near-vision focusing ability is calledpresbyopia, and it typically requires reading glasses (convex lenses) for close work.
• Myopia (near-sightedness): distant objects appear blurred, due to elongated eyeball or excess curvature — not age-related.
• Hypermetropia (far-sightedness): near objects appear blurred, due to shortened eyeball — can occur at any age.
• Astigmatism: irregular curvature of the cornea/lens causing blurred vision at all distances.
• Presbyopia: age-related weakening of ciliary muscles reducing accommodation power — exactly as described.
Correct Answer: Presbyopia
RRB Group D 2025-26 – 14 August 2026 Shift 2 · Power of accommodation, near point and far point

Q11. Which of the following best describes the power of accommodation of the human eye?

  1. (a) The adjustment of eyelid position for better vision
  2. (b) The ability of the eye lens to change its focal length to focus on objects at different distances
  3. (c) The ability of the pupil to change size with light intensity
  4. (d) The movement of the eyeball to follow moving objects
Answer & solution

Answer: (b) The ability of the eye lens to change its focal length to focus on objects at different distances

Answer: Option 2 – The ability of the eye lens to change its focal length to focus at different distances.
•Accommodationis the eye lens adjusting its focal length via the ciliary muscles.
RRB Group D 2025-26 – 14 August 2026 Shift 3 · Prism and dispersion of light

Q12. Why does white light split into different colours when passing through a prism but not when passing through a glass slab?

  1. (a) Because a prism is transparent
  2. (b) Because a prism is made of a different material
  3. (c) Because a prism has non-parallel sides
  4. (d) Because a prism is thinner than a slab
Answer & solution

Answer: (c) Because a prism has non-parallel sides

Answer: Option 3 – Because a prism has non-parallel sides.
• A prism'snon-parallel facesdeviate colours by different amounts, dispersing white light; a glass slab's parallel faces recombine them.
RRB Group D 2025-26 – 13 August 2026 Shift 1 · Structure and parts of the human eye

Q13. Which part of the human eye controls the amount of light entering the eye?

  1. (a) Optic Nerve
  2. (b) Iris
  3. (c) Retina
  4. (d) Cornea
Answer & solution

Answer: (b) Iris

Answer: Option 2 – Iris.
• Theirisadjusts the pupil size, controlling the light entering the eye.
RRB Group D 2025-26 – 13 August 2026 Shift 2 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q14. What is the primary reason stars appear to twinkle in the night sky as seen from Earth?

  1. (a) The light from stars is refracted by varying atmospheric layers
  2. (b) Stars emit light at varying intensities
  3. (c) The Earth rotates causing starlight to flicker
  4. (d) Stars are closer to the Earth than planets
Answer & solution

Answer: (a) The light from stars is refracted by varying atmospheric layers

Answer: Option 1 – The light from stars is refracted by varying atmospheric layers.
• Twinkling is due toatmospheric refractionof starlight through layers of varying density.
RRB Group D 2025-26 – 12 August 2026 Shift 3 · Prism and dispersion of light

Q15. Why do the seven colors of sunlight emerge separately after passing through a prism?

  1. (a) All colors move at the same speed in glass
  2. (b) Colors are absorbed at different rates
  3. (c) Different colors travel at different speeds in glass
  4. (d) Prism shape blocks some colors
Answer & solution

Answer: (c) Different colors travel at different speeds in glass

Answer: Option 3 – Different colours travel at different speeds in glass.
• Colours refract by different amounts because they havedifferent speeds in glass⇒ dispersion.
RRB Group D 2025-26 – 11 August 2026 Shift 1 · Prism and dispersion of light

Q16. A teacher uses two prisms placed in opposite orientations and passes a beam of white light through both. What is the expected outcome on a screen placed after the second prism?

  1. (a) A new set of colors emerge beyond the original ones
  2. (b) A single white patch appears on the screen
  3. (c) A spectrum with reversed color order forms
  4. (d) A black region appears where the beam ends
Answer & solution

Answer: (b) A single white patch appears on the screen

Answer: Option 2 – A single white patch appears on the screen.
• The second inverted prismrecombinesthe dispersed colours, giving back a patch ofwhite light.
RRB Group D 2025-26 – 11 August 2026 Shift 2 · Prism and dispersion of light

Q17. What is the angle between the incident and emergent rays called in the context of a prism?

  1. (a) The angle of refraction
  2. (b) The angle of deviation
  3. (c) The angle of emergence
  4. (d) The angle of incidence
Answer & solution

Answer: (b) The angle of deviation

Answer: Option 2 – The angle of deviation.
• The angle between the incident and emergent rays of a prism is theangle of deviation.
RRB Group D 2025-26 – 10 August 2026 Shift 2 · Prism and dispersion of light

Q18. A beam of white light passes through a glass prism and splits into different colors. Which physical phenomenon is primarily responsible for the separation of colors after refraction through the prism?

  1. (a) Reflection of light
  2. (b) Dispersion of light
  3. (c) Absorption of light
  4. (d) Scattering of light
Answer & solution

Answer: (b) Dispersion of light

Answer: Option 2 – Dispersion of light.
• A prism splits white light into its colours because different colours refract by different amounts (violet most, red least). This splitting is calleddispersion.
RRB Group D 2025-26 – 10 August 2026 Shift 2 · Defects of vision and their correction

Q19. Which defect of vision is caused by the eye's lens focusing images in front of the retina, making distant objects appear blurry, and can be corrected using a concave lens?

  1. (a) Presbyopia
  2. (b) Astigmatism
  3. (c) Hypermetropia
  4. (d) Myopia
Answer & solution

Answer: (d) Myopia

Answer: Option 4 – Myopia.
•Myopia (short-sightedness): the image of a distant object formsin front of the retina; distant objects look blurred. It is corrected with aconcave (diverging) lens.
RRB Group D 2025-26 – 9 August 2026 Shift 3 · Power of accommodation, near point and far point

Q20. Which application uses refraction to focus light onto a specific point for clear vision?

  1. (a) The human eye lens adjusting its shape
  2. (b) A glass prism splitting sunlight
  3. (c) A plane mirror reflecting images
  4. (d) A shadow formed behind an object
Answer & solution

Answer: (a) The human eye lens adjusting its shape

Answer: Option 1 — The human eye lens adjusting its shape
The eye lens usesrefraction (accommodation)to focus light on the retina → Option 1.
RRB Group D 2025-26 – 9 August 2026 Shift 3 · Prism and dispersion of light

Q21. The refracted ray inside the prism bends ________.

  1. (a) Toward the base of the prism
  2. (b) Perpendicular to the base
  3. (c) Away from the base
  4. (d) Along the base
Answer & solution

Answer: (a) Toward the base of the prism

Answer: Option 1 — Toward the base of the prism
Inside a prism, the refracted ray bendstoward the base→ Option 1.
RRB Group D 2025-26 – 6 August 2026 Shift 1 · Power of accommodation, near point and far point

Q22. What is the ability of the eye lens to adjust its focal length called?

  1. (a) Refraction
  2. (b) Myopia
  3. (c) Persistence of vision
  4. (d) Power of Accommodation
Answer & solution

Answer: (d) Power of Accommodation

Answer: Option 4 — Power of Accommodation
The eye lens's ability to change focal length is thepower of accommodation→ Option 4.
RRB Group D 2025-26 – 6 August 2026 Shift 2 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q23. How does the size of atmospheric particles affect the scattering of sunlight?

  1. (a) Smaller particles scatter shorter wavelengths more efficiently
  2. (b) Medium particles scatter only green light efficiently
  3. (c) Irregular particles scatter only yellow light more
  4. (d) Larger particles scatter only red light effectively
Answer & solution

Answer: (a) Smaller particles scatter shorter wavelengths more efficiently

Answer: Option 1 — Smaller particles scatter shorter wavelengths more efficiently
Rayleigh scattering:small particles scatter short (blue) wavelengths more→ Option 1.
RRB Group D 2025-26 – 6 August 2026 Shift 3 · Prism and dispersion of light

Q24. What is the angle between the two lateral faces of a triangular glass prism called?

  1. (a) The angle of incidence.
  2. (b) The angle of refraction.
  3. (c) The angle of deviation.
  4. (d) The angle of the prism.
Answer & solution

Answer: (d) The angle of the prism.

Answer: Option 4 — The angle of the prism
The angle between the two lateral (refracting) faces is theangle of the prism→ Option 4.
RRB Group D 2025-26 – 5 August 2026 Shift 1 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q25. Which phenomenon best explains why the sky appears blue during daytime?

  1. (a) Shorter wavelengths of sunlight are scattered more than longer wavelengths
  2. (b) Sun emits predominantly blue light during the day
  3. (c) Reflection of sunlight by clouds causes blue color
  4. (d) Ozone in the atmosphere absorbs all other colors except blue
Answer & solution

Answer: (a) Shorter wavelengths of sunlight are scattered more than longer wavelengths

Answer: Option 1 — Shorter wavelengths are scattered more
Blue (shorter wavelength) light scatters more than red (Rayleigh scattering), so the sky looks blue → Option 1.
RRB Group D 2025-26 – 5 August 2026 Shift 2 · Prism and dispersion of light

Q26. Which of the following statements about dispersion of light are true?
(1) While passing through a glass prism, red light bends the most.
(2) The angle of deviation is the same for all colours.
(3) Dispersion is one of the phenomena responsible for the formation of a rainbow.
(4) The speed of light decreases when it enters a prism from air.

  1. (a) Only statements 1 and 3
  2. (b) Only statements 1 and 2
  3. (c) Only statements 2 and 4
  4. (d) Only statements 3 and 4
Answer & solution

Answer: (d) Only statements 3 and 4

Answer: Option 4 — Only statements 3 and 4
(1) False — red light bends theleast(violet bends most). (2) False — deviation differs with colour. (3) True — dispersion helps form a rainbow. (4) True — light slows entering glass. So3 and 4→ Option 4.
*(Translated from Bengali; solved in English.)*
RRB Group D 2025-26 – 5 August 2026 Shift 2 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q27. A science museum plans an exhibit explaining why the sky looks blue during the day but takes on a reddish tinge at sunrise and sunset. Based on the scattering of light in the atmosphere, which explanation gives the most correct reason for this observation?

  1. (a) The Sun emits more blue light during the day and more red light at sunset.
  2. (b) Dust particles scatter all wavelengths equally, and increased dust at sunset makes red light more visible.
  3. (c) Atmospheric absorption removes red light during the day and blue light at sunset.
  4. (d) Shorter wavelengths are scattered more strongly, while at sunset the longer atmospheric path favours the longer (red) wavelengths.
Answer & solution

Answer: (d) Shorter wavelengths are scattered more strongly, while at sunset the longer atmospheric path favours the longer (red) wavelengths.

Answer: Option 4 — Shorter wavelengths scatter more; at sunset the longer path favours red
Blue (shorter λ) scatters more, so the daytime sky is blue. At sunrise/sunset light travels alonger atmospheric path, scattering out blue and leaving theredto reach us → Option 4.
*(Translated from Bengali; solved in English.)*
RRB Group D 2025-26 – 4 August 2026 Shift 1 · Prism and dispersion of light

Q28. What would happen to the spread of colors in the spectrum if a second identical prism is placed after the first in an inverted position?

  1. (a) Only red and violet merge
  2. (b) The spread of colors recombines to form white light
  3. (c) The colors spread further apart
  4. (d) The spectrum shifts to one side
Answer & solution

Answer: (b) The spread of colors recombines to form white light

Answer: Option 2 — The spread of colours recombines to form white light
A second, inverted identical prismrecombinesthe dispersed colours back intowhite light→ Option 2.
RRB Group D 2025-26 – 4 August 2026 Shift 2 · Prism and dispersion of light

Q29. When a ray of light passes through a triangular glass prism, the emergent ray is generally not parallel to the incident ray. Which of the following best explains this observation?

  1. (a) The light ray passes through the prism uniformly without any change in direction.
  2. (b) The light ray undergoes complete reflection at both faces of the prism.
  3. (c) The parallel faces of the prism produce equal refractions that cancel each other.
  4. (d) The two refracting faces of the prism are inclined to each other, causing an overall deviation of the light ray.
Answer & solution

Answer: (d) The two refracting faces of the prism are inclined to each other, causing an overall deviation of the light ray.

Answer: Option 4 — The two refracting faces are inclined, causing an overall deviation
A prism's two faces arenot parallel(they are inclined), so the two refractions add up to a netdeviation, and the emergent ray is not parallel to the incident ray → Option 4.
RRB Group D 2025-26 – 4 August 2026 Shift 3 · Defects of vision and their correction

Q30. Which defect occurs when the eye lens loses its ability to focus on near objects due to decreased flexibility?

  1. (a) Myopia results from reduced lens flexibility
  2. (b) Astigmatism results from reduced lens flexibility
  3. (c) Hypermetropia results from reduced lens flexibility
  4. (d) Presbyopia results from reduced lens flexibility
Answer & solution

Answer: (d) Presbyopia results from reduced lens flexibility

Answer: Option 4 — Presbyopia
Presbyopiais the age-related loss of the lens's flexibility (accommodation), reducing near vision → Option 4.
RRB Group D 2025-26 – 4 August 2026 Shift 3 · Prism and dispersion of light

Q31. What happens when white light passes through a glass prism?

  1. (a) It becomes invisible
  2. (b) It splits into a band of seven colours
  3. (c) It recombines into white light
  4. (d) It changes into a single colour
Answer & solution

Answer: (b) It splits into a band of seven colours

Answer: Option 2 — It splits into a band of seven colours
White lightdispersesinto a spectrum of seven colours through a prism → Option 2.
RRB Group D 2025-26 – 3 August 2026 Shift 1 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q32. Why does the sky appear blue to human observers during daytime?

  1. (a) Red light is scattered more than blue light due to its longer wavelength
  2. (b) Blue light is absorbed and re-emitted by atmospheric particles
  3. (c) All wavelengths are scattered equally in the atmosphere
  4. (d) Blue light is scattered more than red light due to its shorter wavelength
Answer & solution

Answer: (d) Blue light is scattered more than red light due to its shorter wavelength

Answer: Option 4 — Blue light is scattered more than red light due to its shorter wavelength
Concept (Rayleigh scattering):Scattering ∝ 1/λ⁴. Blue light has ashorter wavelength, so it is scattered much more than red by air molecules. This scattered blue light reaching our eyes makes the daytime sky look blue → Option 4.
RRB NTPC UG CBT-1 2025-26 – 15 June 2026 Shift 1 · Defects of vision and their correction

Q33. Which optical instrument is used to correct the eye defect known as Hypermetropia (or long-sightedness), where light focuses behind the retina?

  1. (a) Concave Lens
  2. (b) Photochromic Lenses
  3. (c) Cylindrical Lens
  4. (d) Convex Lens
Answer & solution

Answer: (d) Convex Lens

Hypermetropia (Long-sightedness)
Defect: Light focusesbehind the retina
Cause: Eyeball too short or lens has weak converging power
Correction: Need to converge light raysbeforeentering eye
Convex lens(converging lens) is used
Convex lens increases converging power → brings focus onto retina
Answer: Option 4 → Convex Lens
SSC GD 2026 – 31 May 2026 Shift 1 · Structure and parts of the human eye

Q34. What is the approximate diameter of the human eyeball?

  1. (a) 1.3 cm
  2. (b) 2.3 cm
  3. (c) 3.3 cm
  4. (d) 4.3 cm
Answer & solution

Answer: (b) 2.3 cm

Correct Answer: 2.3 cm (Option 2)
The human eyeball (globe) has an approximate diameter of 2.3 to 2.5 cm (about 1 inch). It is a roughly spherical organ housed in the orbital socket of the skull. The eyeball contains the cornea, iris, lens, vitreous humor, and retina, all working together to focus light and enable vision.
Why others are wrong:
- 1.3 cm: Too small — this would be the size of a very small organ, not an adult human eye.
- 3.3 cm: Too large for a human eyeball.
- 4.3 cm: Significantly larger than the actual size of a human eye.
SSC GD 2026 – 30 May 2026 Shift 3 · Defects of vision and their correction

Q35. Which method is commonly used to treat cataracts in the human eye?

  1. (a) Eye drops
  2. (b) Eye exercises
  3. (c) Surgery
  4. (d) Spectacles
Answer & solution

Answer: (c) Surgery

Correct Answer: Surgery (Option 3)
A cataract is the clouding of the natural lens of the eye, which blocks or blurs light passing to the retina. The standard and most effective treatment for cataracts is surgical removal of the cloudy lens, which is then replaced with an artificial intraocular lens (IOL). This is one of the most commonly performed and safe surgical procedures worldwide.
Why others are wrong:
- Eye drops: No medically approved eye drops can dissolve or reverse cataracts.
- Eye exercises: Exercises cannot restore the clarity of a clouded lens.
- Spectacles: Glasses can temporarily compensate for early vision loss due to cataracts but cannot cure the condition.
SSC GD 2026 – 27 May 2026 Shift 2 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q36. ______ can be observed when a fine beam of light enters a room through small holes.

  1. (a) Tyndall Effect
  2. (b) Brownian Motion
  3. (c) Diffraction
  4. (d) Deposition
Answer & solution

Answer: (a) Tyndall Effect

Correct Answer: Tyndall Effect — Option (a)
The Tyndall Effect is observed when a fine beam of light enters a room through small holes, making the light beam visible. About the Tyndall Effect: Discovered/described by: John Tyndall (1820-1893), Irish physicist; Definition: The scattering of light by colloidal particles suspended in a medium, making the path of light visible; Why it occurs: When light passes through a colloidal solution or medium with suspended particles (like dust in air), the particles scatter light in all directions; This makes the beam of light visible from the side — the beam appears as a luminous cone; Examples of Tyndall Effect: A beam of light entering a dark room through small holes — dust particles scatter the light, making the beam visible; Sunlight through clouds (crepuscular rays/God's rays); Car headlights in fog — the beam becomes visible; Light through milk or colloidal solutions in lab; Blue color of the sky is due to Rayleigh scattering (similar concept); Smoke from a chimney appearing blue in certain lighting; Tyndall vs Rayleigh Scattering: Tyndall Effect: Involves larger colloidal particles; non-selective scattering; Rayleigh Scattering: Involves very small molecules (like air molecules); selective (blue light scattered more); About other options: Brownian Motion: Random motion of colloidal particles due to collision with solvent molecules — NOT related to light beams in rooms; Diffraction: Bending of light around obstacles/through small openings — this IS related to small holes, but the visible beam in a room is primarily due to Tyndall Effect; Deposition: Sedimentation or geological deposition — has no relation to light beams.
Option (b) Brownian Motion — Incorrect: Brownian Motion is the random, erratic movement of colloidal particles (like pollen grains in water) caused by collision with solvent/medium molecules; it was discovered by Robert Brown in 1827 and explained by Einstein in 1905; it is NOT what makes a beam of light visible when entering a room through small holes — that is the Tyndall Effect.
Option (c) Diffraction — Incorrect: Diffraction refers to the bending of light (or other waves) around obstacles or through small openings; while diffraction does occur when light passes through small holes (creating diffraction patterns), the phenomenon that makes the light beam VISIBLE as a cone of light in a dusty room is the Tyndall Effect (scattering by dust particles); the candidate selected this incorrect option.
Option (d) Deposition — Incorrect: Deposition in physics/geology refers to the settling of sediment or the phase transition from gas directly to solid (like frost formation); it has absolutely no connection to the phenomenon of a light beam being visible when it enters a room through small holes; that phenomenon is the Tyndall Effect — scattering of light by colloidal/dust particles.
SSC GD 2026 – 5 May 2026 Shift 1 · Defects of vision and their correction

Q37. A common type of bifocal lens contains ___.

  1. (a) Two concave lenses
  2. (b) Two convex lenses
  3. (c) One concave and one convex lens
  4. (d) Two cylindrical lenses
Answer & solution

Answer: (c) One concave and one convex lens

Correct Answer: One concave and one convex lens — Option (c)
A bifocal lens is a corrective eyeglass lens that contains two distinct optical powers. The upper portion is typically a concave lens (for distance vision — correcting myopia/short-sightedness), while the lower portion is a convex lens (for near vision — correcting presbyopia/reading difficulty). This combination allows the wearer to see clearly at both distant and close ranges without switching glasses.
Option (a) Two concave lenses — Incorrect: Two concave lenses would only correct myopia at both segments, not serve a bifocal purpose.
Option (b) Two convex lenses — Incorrect: Two convex lenses would only correct hypermetropia/reading difficulty, not serve a bifocal purpose.
Option (d) Two cylindrical lenses — Incorrect: Cylindrical lenses correct astigmatism; they are not the standard components of a bifocal lens.
SSC GD 2026 – 4 May 2026 Shift 3 · Rainbow formation

Q38. A student sees a rainbow just after rain. If they try to move closer to the rainbow, what will happen?

  1. (a) They will reach the rainbow
  2. (b) The rainbow will disappear
  3. (c) The rainbow will appear at the same distance
  4. (d) The rainbow will change colors
Answer & solution

Answer: (c) The rainbow will appear at the same distance

Correct Answer: The rainbow will appear at the same distance — Option (c)
A rainbow is an optical phenomenon caused by the refraction, dispersion, and reflection of sunlight in water droplets. It has no fixed physical location — it appears at a specific angle (42° for red light) relative to the observer's line of sight to the sun. No matter how far the observer moves toward the rainbow, it will always appear to remain at the same apparent distance. This is because the rainbow moves with the observer as they move.
Option (a) They will reach the rainbow — Incorrect: A rainbow cannot be physically reached; it is not a fixed object in space.
Option (b) The rainbow will disappear — Incorrect: Moving toward a rainbow does not make it vanish; it stays at the same apparent distance.
Option (d) The rainbow will change colors — Incorrect: Moving toward a rainbow does not change its colors; the spectral order (VIBGYOR) remains the same.
RRB NTPC GL CBT-1 2025-26 – 16 March 2026 Shift 2 · Prism and dispersion of light

Q39. The formation of a spectrum by a glass prism occurs due to ________.

  1. (a) Dispersion
  2. (b) Scattering
  3. (c) Reflection
  4. (d) Refraction
Answer & solution

Answer: (a) Dispersion

When white light passes through a glass prism, it splits into a spectrum of seven colours (VIBGYOR).
This happens due to DISPERSION.
Why Dispersion?
• Different colours (wavelengths) of light travel at different speeds in glass.
• Each colour bends (refracts) by a different amount at the glass surface.
• Violet bends most, Red bends least (VBGYOR order of deviation).
Difference with other options:
• Scattering → why sky is blue (Rayleigh scattering of sunlight).
• Reflection → light bouncing back from a surface.
• Refraction → bending of light at one interface (not splitting into spectrum).
Answer: Option 1 → Dispersion
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 1 · Defects of vision and their correction

Q40. The far point of a myopic person is 80 cm in front of the eye. Assuming the far point for normal vision is infinity, what is the required power (P) of the corrective lens?

  1. (a) +0.80 D
  2. (b) -1.25 D
  3. (c) +1.25 D
  4. (d) -0.80 D
Answer & solution

Answer: (b) -1.25 D

The far point of the myopic eye is 80 cm, so the lens must make distant objects appear at 80 cm.
Use lens formula: Power P = -100 / far point distance in cm for myopia.
P = -100 / 80 = -1.25 Diopters.
The negative sign indicates a concave lens is required.
Hence, the corrective lens power is -1.25 D.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 2 · Prism and dispersion of light

Q41. Which of the following statement(s) is/are true when a beam of white light is incident on a glass prism?
(i) The white light undergoes dispersion.
(ii) The speed of light remains constant when it goes from air into the prism.
(iii) The speed of light decreases as the light goes from air into the prism.

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

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

Correct option is 4.
(i) When white light passes through a glass prism, it splits into its constituent colours due to dispersion. This is true.
(ii) The speed of light does not remain constant when it goes from air into the prism. It changes due to the refractive index of glass.
(iii) The speed of light decreases when it goes from air (a less dense medium) into the glass prism (a denser medium). This is true.
Hence, only statements (i) and (iii) are correct.
RRB Technician Grade III 2025-26 – 10 March 2026 Shift 2 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q42. Why does the sky appear dark to passengers flying at very high altitudes?

  1. (a) They are above the atmosphere.
  2. (b) The air molecules absorb all blue light at that altitude.
  3. (c) The path of light is scattered back towards the sun.
  4. (d) Scattering of light is not prominent at such heights.
Answer & solution

Answer: (d) Scattering of light is not prominent at such heights.

The sky appears blue due to Rayleigh scattering in the Earth's atmosphere.
At very high altitudes, the atmosphere is very thin, so scattering of sunlight is minimal.
With less scattering of light, the sky appears black or very dark.
Hence, passengers flying at very high altitudes see a dark sky because scattering of light is not prominent at such heights.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 3 · Prism and dispersion of light

Q43. In a prism, the emergent ray comes out at an angle different from the incident ray. What is this angle called?

  1. (a) Angle of reflection
  2. (b) Angle of incidence
  3. (c) Angle of the prism
  4. (d) Angle of deviation
Answer & solution

Answer: (d) Angle of deviation

The emergent ray differs in direction from the incident ray after passing through the prism.
This difference in direction is referred to as the angle of deviation.
Thus, the angle between the incident ray and the emergent ray is called the angle of deviation.
Hence, the correct answer is option 4.
RRB Technician Grade III 2025-26 – 9 March 2026 Shift 3 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q44. The main reason for twinkling of stars is _________.

  1. (a) Nuclear reactions inside stars
  2. (b) Scattering of star light
  3. (c) Atmospheric refraction varying with time
  4. (d) Presence of clouds
Answer & solution

Answer: (c) Atmospheric refraction varying with time

The twinkling of stars occurs because their light passes through Earth's atmosphere.
Atmospheric refraction causes the light to bend slightly while moving through air layers of varying density.
These variations are not constant and change rapidly, making the star light appear to flicker or twinkle.
Hence, the cause is the atmospheric refraction varying with time, not any process inside the star or scattering or clouds directly.
This explains why planets generally do not twinkle, as they appear as disks, less affected by refraction.
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 3 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q45. When we observe a star near the horizon, it appears to be slightly higher in the sky than it really is. What is the reason for this?

  1. (a) The star moves rapidly and changes its position.
  2. (b) The atmosphere bends the starlight due to gradual changes in refractive index.
  3. (c) The Earth's rotation shifts the star upward.
  4. (d) The star becomes brighter, making it seem higher.
Answer & solution

Answer: (b) The atmosphere bends the starlight due to gradual changes in refractive index.

Correct option: 2
The star appears higher near the horizon due to atmospheric refraction.
Earth's atmosphere has layers with gradually changing refractive index.
Light from the star bends when it passes through these layers.
This bending causes the star's apparent position to shift upward.
Hence, we see the star slightly higher than its true position.
This phenomenon is well known as atmospheric refraction.
Options 1, 3, and 4 are incorrect because star position and brightness do not cause this apparent shift.
Final answer: Option 2
RRB Technician Grade III 2025-26 – 6 March 2026 Shift 2 · Prism and dispersion of light

Q46. When white light is incident obliquely on a glass prism, which of the following statement(s) is/are NOT true?
(i) Red colour undergoes minimum deviation.
(ii) The speed of violet colour is the least while travelling through the prism.
(iii) Refractive index of green colour is more than the violet colour.
(iv) Refractive index of red colour is more than blue colour.

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

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

Option 4 is correct.
(i) Red colour undergoes minimum deviation − True, because deviation is least for red light in a prism due to its lower refractive index.
(ii) The speed of violet colour is the least while travelling through the prism − True, because violet light has the highest refractive index, so it travels slowest.
(iii) Refractive index of green colour is more than the violet colour − False, violet has higher refractive index than green.
(iv) Refractive index of red colour is more than blue colour − False, red has lower refractive index than blue.
Hence, statements (iii) and (iv) are NOT true.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 1 · Defects of vision and their correction

Q47. A young child is diagnosed with both myopia and hypermetropia in different eyes. What is the most appropriate corrective approach?

  1. (a) Providing glasses with different lenses for each eye (concave for one, convex for the other)
  2. (b) Using bifocal lenses in both eyes
  3. (c) Using cylindrical lenses in both eyes
  4. (d) Providing identical convex lenses for both eyes
Answer & solution

Answer: (a) Providing glasses with different lenses for each eye (concave for one, convex for the other)

A child diagnosed with myopia (nearsightedness) in one eye and hypermetropia (farsightedness) in the other requires different lens types for each eye.
Myopia is corrected by concave lenses that diverge light rays.
Hypermetropia is corrected by convex lenses that converge light rays.
Therefore, the child must be given glasses with different lenses for each eye: concave for myopic eye, convex for hypermetropic eye.
This corrects vision in both eyes appropriately.
Final answer: Option 1
RRB JE CBT-1 2025-26 – 20 February 2026 Shift 3 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q48. If atmospheric refraction did not occur, which change would be most noticeable during the observation of stars from Earth?

  1. (a) Stars would change color rapidly.
  2. (b) Stars would disappear from the night sky.
  3. (c) Planets would twinkle like stars.
  4. (d) Stars would not twinkle; their light would remain steady.
Answer & solution

Answer: (d) Stars would not twinkle; their light would remain steady.

Atmospheric refraction causes the bending of starlight as it passes through Earth's atmosphere.
This bending leads to the apparent twinkling (scintillation) of stars.
Without atmospheric refraction, starlight would not bend or be distorted.
Therefore, stars would not appear to twinkle but shine with a steady light.
Planets do not twinkle much because they have a larger apparent size, averaging out atmospheric effects.
Hence, the most noticeable change would be the disappearance of the twinkling effect in stars.
Correct answer is option 4.
Answer complete.
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 2 · Defects of vision and their correction

Q49. A person with both myopia and hypermetropia is most likely to use which type of lens?

  1. (a) Convex lens
  2. (b) Concave lens
  3. (c) Cylindrical lens
  4. (d) Bi-focal lens
Answer & solution

Answer: (d) Bi-focal lens

A person with myopia (nearsightedness) needs a concave lens to correct vision.
A person with hypermetropia (farsightedness) needs a convex lens to correct vision.
Having both conditions means the person needs correction for both near and far vision.
A bi-focal lens combines both concave and convex lenses to correct these simultaneously.
Hence, the person most likely uses bi-focal lenses for clear vision at all distances.
Final answer: Option 4
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 3 · Prism and dispersion of light

Q50. A scientist wants to demonstrate that dispersion depends on wavelength. She shines monochromatic red light through a prism. What does she observe and why?

  1. (a) Red light is absorbed, so nothing emerges
  2. (b) Only a single red ray emerges; no spectrum forms because there is only one wavelength
  3. (c) A full spectrum appears, showing all colors
  4. (d) Multiple red rays emerge, each at a different angle
Answer & solution

Answer: (b) Only a single red ray emerges; no spectrum forms because there is only one wavelength

Correct option: 2
Dispersion occurs when white light splits into multiple colours due to different wavelengths refracting differently.
Monochromatic light, like red light, has only one wavelength.
When red light passes through a prism, it refracts but does not split into a spectrum.
Thus, only a single red ray emerges, without forming a spectrum.
This shows dispersion depends on multiple wavelengths, which are absent here.
Hence, the scientist observes a single red ray emerging from the prism without a spectrum.
Answer complete.
RRB JE CBT-1 2025-26 – 19 February 2026 Shift 1 · Structure and parts of the human eye

Q51. What is the function of the iris in the human eye?

  1. (a) Controls the size of the pupil
  2. (b) Transmits signals to the brain
  3. (c) Refracts incoming light rays
  4. (d) Forms the image on the retina
Answer & solution

Answer: (a) Controls the size of the pupil

The iris is the coloured part of the eye.
It controls the size of the pupil by contracting or dilating.
This regulation adjusts the amount of light entering the eye.
Hence, the iris functions to control the pupil size, adapting to light conditions.
Option 1 is correct.
Answer complete.
SSC MTS 2025 – 13 February 2026 Shift 1 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q52. In which natural setting can the Tyndall effect be observed?

  1. (a) Sunlight passing through a window
  2. (b) Sunlight passing through the canopy of a dense forest
  3. (c) A rainbow after a rainstorm
  4. (d) Light reflected from a mirror
Answer & solution

Answer: (b) Sunlight passing through the canopy of a dense forest

Correct Answer: Option 2 – Sunlight passing through the canopy of a dense forest
The Tyndall effect is the scattering of light by colloidal particles (particles larger than molecules but not visible to the naked eye). In a dense forest, sunlight passes through the canopy and becomes visible as beams of light due to the scattering by dust, water droplets, and small particles in the air. This is the classic natural observation of the Tyndall effect.
Why other options are wrong:
Option 1 (Sunlight through a window): Plain window glass does not contain colloidal particles to scatter light; Tyndall effect is not typically observed here.
Option 3 (Rainbow after a rainstorm): A rainbow is caused by refraction and reflection of light in raindrops — it is a different phenomenon (dispersion of light), not Tyndall effect.
Option 4 (Light reflected from a mirror): Reflection from a mirror is specular reflection, not related to Tyndall effect.
Delhi Police Head Constable (Ministerial) 2025-26 – 10 January 2026 Shift 1 · Rainbow formation

Q53. What is the main cause for the formation of a rainbow?

  1. (a) Reflection
  2. (b) Refraction and dispersion
  3. (c) Interference
  4. (d) Diffraction
Answer & solution

Answer: (b) Refraction and dispersion

A rainbow is formed when sunlight enters water droplets in the atmosphere. The light undergoes refraction (bending) at entry, then internal reflection inside the droplet, and refraction again on exit. During refraction, white light is dispersed into its constituent colours (VIBGYOR — Violet, Indigo, Blue, Green, Yellow, Orange, Red), creating the rainbow.
(1) Reflection alone does not cause a rainbow; refraction and dispersion are essential components.
(3) Interference is a wave phenomenon causing patterns like thin-film iridescence (e.g., soap bubbles), not rainbows.
(4) Diffraction involves bending of waves around obstacles or through slits, not the cause of rainbows.
SSC CGL Tier-1 2025 – 24 September 2025 Shift 1 · Rainbow formation

Q54. The color order in a secondary rainbow is:

  1. (a) Same as primary rainbow
  2. (b) Reversed compared to primary rainbow
  3. (c) Random and variable
  4. (d) Depends on humidity
Answer & solution

Answer: (b) Reversed compared to primary rainbow

A secondary rainbow is formed by two internal reflections of sunlight inside raindrops, while a primary rainbow involves one internal reflection.
Due to the extra reflection, the order of colours in a secondary rainbow is reversed (red inside, violet outside) compared to the primary rainbow.
SSC CGL Tier-1 2025 – 15 September 2025 Shift 3 · Power of accommodation, near point and far point

Q55. The least distance of distinct vision for a normal human eye is approximately:

  1. (a) 2.5 cm
  2. (b) 25 cm
  3. (c) 2.5 m
  4. (d) 25 m
Answer & solution

Answer: (b) 25 cm

• The least distance of distinct vision (Near Point) for a normal healthy human eye = 25 cm.
• This is the minimum distance at which the eye can see an object clearly without strain.
• Objects closer than 25 cm appear blurred to a normal eye.
• For elderly persons (presbyopia), this distance increases beyond 25 cm.
• Answer: 25 cm
SSC Selection Post 2025 (Phase XIII) – 1 August 2025 Shift 3 · Structure and parts of the human eye

Q56. What happens to the pupil in low light conditions?

  1. (a) It contracts to prevent excess light from entering
  2. (b) It expands to allow more light to enter
  3. (c) It remains the same size
  4. (d) It changes color
Answer & solution

Answer: (b) It expands to allow more light to enter

Correct Answer: Option 2 – It expands to allow more light to enter
In low light conditions, the pupil dilates (expands/widens) to allow maximum light to enter the eye, enabling better vision in dim conditions. This is controlled by the dilator pupillae muscle, which is activated by the sympathetic nervous system.
Option 1 (Contracts): The pupil contracts (constricts) in bright light to protect the retina from excess light.
Option 3 (Remains same size): Incorrect; the pupil size actively changes with light levels.
Option 4 (Changes color): The iris (which surrounds the pupil) has color; the pupil itself is an opening and does not change color.
RRB Technician Grade III 2024-25 – 30 December 2024 Shift 3 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q57. The danger signal lights are usually red in colour because red is:

  1. (a) not scattered at all by fog or smoke
  2. (b) least scattered by fog or smoke
  3. (c) highest scattered by fog or smoke
  4. (d) highest reflected by fog or smoke
Answer & solution

Answer: (b) least scattered by fog or smoke

Correct Answer: Option 2 — least scattered by fog or smoke
When light passes through fog, smoke or dust, its rays are scattered sideways by the tiny suspended particles. According to Rayleigh's law of scattering, the amount of scattering varies inversely as the fourth power of the wavelength:
Scattering ∝ 1/λ⁴
Red light has the longest wavelength in the visible spectrum (about 620–750 nm), so it is scattered the least of all colours. A red beam therefore travels the greatest distance through fog or smoke without being spread out, and remains visible from far away.
That is exactly why danger signals, traffic stop lights, brake lights and railway signals are red — the driver can see them from a safe stopping distance even in poor visibility. Violet and blue, having the shortest wavelengths, would scatter away long before reaching the observer.
❌ Why the other options are incorrect
✗ not scattered at all by fog or smoke — too strong a statement; red is scattered, only much less than the other colours. No colour escapes scattering completely.
✗ highest scattered by fog or smoke — this is true of violet and blue, not red; a strongly scattered colour would fade quickly and make a poor signal.
✗ highest reflected by fog or smoke — the effect involved here is scattering, not reflection, and a strongly reflected light would be thrown back rather than reaching the observer.
📌 SSC & Railway Exam Facts
• Rayleigh scattering ∝ 1/λ⁴ — shorter wavelength means more scattering.
• Order of wavelength: VIBGYOR, violet shortest (≈400 nm), red longest (≈700 nm).
• The sky looks blue because blue is scattered most; the Sun looks red at sunrise and sunset because the long path lets only red through.
• Danger/stop signals are red; red also has the least deviation in a prism.
• The Tyndall effect is the scattering of light by colloidal particles.
RRB Technician Grade III 2024-25 – 30 December 2024 Shift 3 · Prism and dispersion of light

Q58. Which of the following colours of light is bent through a minimum angle when passing through a glass prism?

  1. (a) Blue
  2. (b) Green
  3. (c) Violet
  4. (d) Yellow
Answer & solution

Answer: (d) Yellow

Correct Answer: Option 4 — Yellow
When white light passes through a glass prism it splits into its seven colours — this is dispersion. The splitting happens because the refractive index of glass is different for different colours: it is largest for violet and smallest for red, since
μ increases as the wavelength λ decreases
A larger refractive index means a larger bending, so the angle of deviation follows the order
Violet > Indigo > Blue > Green > Yellow > Orange > Red
Among the four colours offered — Blue, Green, Violet and Yellow — yellow has the longest wavelength (about 570–590 nm). It therefore has the smallest refractive index in glass and is bent through the minimum angle.
❌ Why the other options are incorrect
✗ Blue — wavelength about 450–495 nm, much shorter than yellow, so blue bends considerably more.
✗ Green — wavelength about 495–570 nm, still shorter than yellow; green deviates more than yellow but less than blue.
✗ Violet — the shortest wavelength (≈400 nm) of all, so it has the largest refractive index and suffers the maximum deviation — the exact opposite of what is asked.
📌 SSC & Railway Exam Facts
• Dispersion order VIBGYOR: violet deviates most, red least.
• Refractive index μ = c/v = sin i / sin r (Snell's law); μ is higher for shorter wavelengths.
• Red has the longest wavelength and the highest speed inside glass; violet the shortest wavelength and the lowest speed.
• Newton first demonstrated dispersion with a prism and recombined the colours with a second, inverted prism.
• A rainbow is formed by refraction, total internal reflection and dispersion of sunlight in water droplets.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 1 · Prism and dispersion of light

Q59. Who among the following scientists was the first to use a glass prism to discover the spectrum of sunlight?

  1. (a) Prof CV Raman
  2. (b) Albert Einstein
  3. (c) Archimedes
  4. (d) Sir Isaac Newton
Answer & solution

Answer: (d) Sir Isaac Newton

Correct Answer: Option 4 — Sir Isaac Newton
Sir Isaac Newton was the first scientist to pass a narrow beam of sunlight through a glass prism and obtain a band of seven colours on a screen. He performed this famous experiment in 1666 in a darkened room at Cambridge and named the coloured band the spectrum. The splitting of white light into its component colours is called dispersion of light.
Newton then did a second, decisive experiment: he placed a second inverted prism in the path of the spectrum and the seven colours recombined into white light. This proved that the colours were already present inside sunlight — the prism only separates them, it does not create them.
Dispersion happens because the refractive index of glass is different for different colours. Violet has the shortest wavelength, so it is refracted the most; red has the longest wavelength, so it is refracted the least. The order of colours is therefore VIBGYOR — Violet, Indigo, Blue, Green, Yellow, Orange, Red.
❌ Why the other options are incorrect
✗ Prof CV Raman — an Indian physicist who discovered the Raman Effect (scattering of light), for which he won the Nobel Prize in 1930; he did not discover the spectrum.
✗ Albert Einstein — known for the photoelectric effect and the theory of relativity, work done more than two centuries after Newton's prism experiment.
✗ Archimedes — an ancient Greek scientist famous for the principle of buoyancy and the lever, not for optics of this kind.
📌 SSC & Railway Exam Facts
• Dispersion of white light through a prism was first shown by Newton (1666); the coloured band is the spectrum.
• Sequence of colours: VIBGYOR; violet bends most, red bends least.
• A rainbow is a natural spectrum formed by refraction + total internal reflection + dispersion in water droplets.
• Refractive index of glass ≈ 1.5, of water ≈ 1.33; the speed of light in vacuum = 3 × 10⁸ m/s.
• CV Raman — Raman Effect (1928), Nobel Prize 1930; National Science Day is celebrated on 28 February.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 2 · Prism and dispersion of light

Q60. In a triangular glass prism, there is/are ____________.

  1. (a) two triangular bases and three rectangular lateral surfaces
  2. (b) three triangular bases and one rectangular lateral surface
  3. (c) one triangular base and three rectangular lateral surfaces
  4. (d) three triangular bases and three rectangular lateral surfaces
Answer & solution

Answer: (a) two triangular bases and three rectangular lateral surfaces

Correct Answer: Option 1 — two triangular bases and three rectangular lateral surfaces
A triangular glass prism is a transparent solid bounded by five plane surfaces in all. Two of them are triangular bases placed parallel to each other at the two ends, and the remaining three are rectangular lateral (side) surfaces that join the corresponding sides of the two triangles. Geometrically it is a triangular prism — a solid with 5 faces, 9 edges and 6 vertices.
When a ray of light enters the prism it refracts twice — once while entering the glass and once while leaving it — and because the two refracting surfaces are not parallel, the emergent ray bends away from the original path. This total bending is the angle of deviation (δ), and the angle between the two refracting surfaces is the angle of the prism (A), usually 60° in a standard laboratory prism.
Since different colours of white light have different refractive indices in glass, each colour bends by a different amount and white light splits into VIBGYOR — this is dispersion of light.
❌ Why the other options are incorrect
✗ three triangular bases and one rectangular lateral surface — a prism has only two bases; three triangular bases is geometrically impossible here.
✗ one triangular base and three rectangular lateral surfaces — with a single base the solid would be open; it would not be a closed prism.
✗ three triangular bases and three rectangular lateral surfaces — again wrong, a triangular prism has exactly 2 triangular + 3 rectangular faces.
📌 SSC & Railway Exam Facts
• Dispersion of white light by a prism was first demonstrated by Sir Isaac Newton.
• Violet deviates the most and red the least, because violet has the shortest wavelength.
• The band of colours obtained is called the spectrum; the order is VIBGYOR.
• A rainbow is a natural spectrum formed by refraction, total internal reflection and dispersion in water droplets.
• Refractive index of ordinary glass ≈ 1.5, of water ≈ 1.33.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 3 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q61. If the earth had no atmosphere, then the colour of the sky would be _________.

  1. (a) blue
  2. (b) black
  3. (c) yellow
  4. (d) red
Answer & solution

Answer: (b) black

Correct Answer: Option 2 — black
The sky looks blue only because of the scattering of sunlight by the molecules of the atmosphere. According to Rayleigh's law, the amount of scattering is inversely proportional to the fourth power of the wavelength (scattering ∝ 1/λ⁴). Since blue light has a much shorter wavelength than red, it is scattered far more strongly in all directions, and that scattered blue light reaches our eyes from every part of the sky.
If the Earth had no atmosphere, there would be no molecules or dust particles to scatter the sunlight. Sunlight would then travel in straight lines from the Sun to the ground without being spread sideways, so no light would come to the eye from other directions of the sky. The sky would therefore appear completely black, with the Sun and the stars visible at the same time.
This is exactly what astronauts see: from the Moon, which has practically no atmosphere, the sky is pitch black even during the day.
❌ Why the other options are incorrect
✗ blue — blue is the colour we see because of the atmosphere; remove the atmosphere and the scattering that produces blue disappears.
✗ yellow — the Sun's disc may look yellowish because of scattering, but the sky itself would not turn yellow without an atmosphere.
✗ red — red dominates at sunrise and sunset, when sunlight travels a long path through the atmosphere and most of the blue has been scattered away — again an atmospheric effect.
📌 SSC & Railway Exam Facts
• Rayleigh scattering: intensity ∝ 1/λ⁴ — blue scatters most, red scatters least.
• Sky appears blue, sun looks red at sunrise/sunset, and danger signals are red because red is scattered the least and travels farthest.
• On the Moon the sky is black all day, as it has no atmosphere.
• Tyndall effect — scattering of light by colloidal particles, e.g. sunbeams through a forest canopy or through fog.
• Clouds appear white because their large water droplets scatter all wavelengths almost equally.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q62. Which of the following phenomena is responsible for Tyndall effect?

  1. (a) Dispersion of light
  2. (b) Scattering of light
  3. (c) Reflection of light
  4. (d) Refraction of light
Answer & solution

Answer: (b) Scattering of light

Correct Answer: Option 2 — Scattering of light
The Tyndall effect is the scattering of a beam of light by the particles of a colloid or a suspension, which makes the path of the beam become visible. It was described by the British scientist John Tyndall.
Scattering occurs because the colloidal particles (1–1000 nm) are comparable in size to the wavelength of visible light (about 400–700 nm). Each particle intercepts the light and re-radiates it in all directions, so an observer standing at the side can see the beam. In a true solution the particles are smaller than 1 nm, far too small to scatter light, so a true solution shows no Tyndall effect — this is the standard laboratory test to tell the two apart.
Everyday examples: a sunbeam entering a dusty room, light from a cinema projector in a smoky hall, head-light beams in fog, and sunlight streaming through the canopy of a dense forest (mist).
❌ Why the other options are incorrect
✗ Dispersion of light — the splitting of white light into its seven colours by a prism; it produces the spectrum and the rainbow, not the visible path of a beam.
✗ Reflection of light — the bouncing back of light from a polished surface such as a mirror; it obeys the laws of reflection and makes images, not a glowing beam through a medium.
✗ Refraction of light — the bending of light when it passes from one medium to another because of a change in speed (e.g. a pencil looking bent in water); it explains lenses, not the Tyndall effect.
📌 SSC & Railway Exam Facts
• Tyndall effect is shown by colloids and suspensions; a true solution never shows it.
• Scattering also makes the sky look blue and the Sun red at sunrise and sunset (Rayleigh scattering, ∝ 1/λ⁴).
• Dispersion → prism/rainbow, Refraction → lens/mirage, Reflection → mirror/periscope.
• Danger signals are red because red has the longest wavelength and is scattered the least.
• C. V. Raman won the Nobel Prize (1930) for the Raman effect, another scattering phenomenon.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · Defects of vision and their correction

Q63. The problem of myopia in human eye can be corrected by using:

  1. (a) a convex lens of suitable power
  2. (b) a plain glass plate
  3. (c) a concave lens of suitable power
  4. (d) a convex mirror of suitable focal length
Answer & solution

Answer: (c) a concave lens of suitable power

Correct Answer: Option 3 — a concave lens of suitable power
Myopia, also called near-sightedness or short-sightedness, is the defect in which a person can see nearby objects clearly but distant objects appear blurred. It happens because the image of a far object is formed in front of the retina instead of on it.
The two causes are (a) excessive curvature of the eye lens, which makes its converging power too high, and (b) elongation of the eyeball, which makes the retina sit too far back.
The remedy is to make the rays diverge a little before they reach the eye lens. A concave (diverging) lens of suitable power does exactly this, so the image is pushed back and falls sharply on the retina. The far point of a myopic eye is at a finite distance, not at infinity, and the corrective lens must have its focal length equal to that far-point distance.
❌ Why the other options are incorrect
✗ a convex lens of suitable power — a convex lens converges light further and is used to correct hypermetropia (long-sightedness), where the image falls behind the retina.
✗ a plain glass plate — a plane plate has zero power; it only shifts the ray sideways and cannot change where the image forms.
✗ a convex mirror of suitable focal length — eye defects are corrected with lenses, not mirrors; a convex mirror is used as a rear-view mirror.
📌 SSC & Railway Exam Facts
• Myopia → concave lens; Hypermetropia → convex lens; Presbyopia → bifocal lens.
• Astigmatism is corrected using a cylindrical lens.
• Power of a lens P = 1/f (in metre); SI unit dioptre (D); a concave lens has negative power.
• The least distance of distinct vision for a normal eye is 25 cm; its far point is at infinity.
• The eye focuses by changing the focal length of its lens — this is called accommodation, done by the ciliary muscles.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q64. What causes the wavy appearance of objects seen through a turbulent stream of hot air?

  1. (a) Refraction of light
  2. (b) Interference of light
  3. (c) Absorption of light
  4. (d) Diffraction of light
Answer & solution

Answer: (a) Refraction of light

Correct Answer: Option 1 — Refraction of light
When air is heated — above a fire, above a hot road or above the exhaust of a jet — the hot air becomes less dense (optically rarer) than the cool air around it. These hot and cold layers keep mixing and moving, so the refractive index of the air keeps changing from point to point and from moment to moment.
Light from an object behind this turbulent air therefore passes through layers of continually changing refractive index and gets refracted by continually changing amounts. The path of the light keeps wobbling, so the object appears to shimmer and wave instead of standing still.
The same physics — atmospheric refraction through moving air of varying density — explains the twinkling of stars and the mirage seen on a hot road in summer.
❌ Why the other options are incorrect
✗ Interference of light — interference needs two coherent sources and produces alternate bright and dark fringes, as in a soap film; it does not make objects wobble.
✗ Absorption of light — absorption only makes an object look dimmer or coloured; it cannot change the apparent shape or position.
✗ Diffraction of light — diffraction is the bending of light around an obstacle or slit whose size is comparable to the wavelength; there is no such obstacle in open hot air.
📌 SSC & Railway Exam Facts
• Refraction is caused by the change in speed of light between two media; n = c/v.
• Twinkling of stars and the early sunrise / delayed sunset (by about 2 minutes) are due to atmospheric refraction.
• Planets do not twinkle — they are extended sources, so the flickering averages out.
• A mirage in a desert is due to refraction followed by total internal reflection.
• Scattering (not refraction) explains the blue sky and the red Sun at sunrise and sunset.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q65. Which phenomenon is responsible for the blue colour of the sky?

  1. (a) Scattering of light
  2. (b) Atmospheric refraction
  3. (c) Reflection
  4. (d) Total internal reflection
Answer & solution

Answer: (a) Scattering of light

Correct Answer: Option 1 — Scattering of light
The blue colour of the sky is caused by the scattering of sunlight by the molecules of air and other very fine particles in the atmosphere.
According to Rayleigh's law of scattering, the amount of light scattered is inversely proportional to the fourth power of the wavelength:
Scattering ∝ 1/λ⁴
Blue light has a short wavelength (about 450 nm) while red light has a long wavelength (about 700 nm). Because of the 1/λ⁴ rule, blue is scattered roughly ten times more strongly than red. This scattered blue light reaches our eyes from every direction of the sky, so the sky looks blue.
The same law explains why the Sun looks red at sunrise and sunset — the light then travels through a much thicker layer of air, all the blue is scattered away and only the red reaches us. For an astronaut, where there is no atmosphere, the sky appears black.
❌ Why the other options are incorrect
✗ Atmospheric refraction — this explains the twinkling of stars and the apparent early sunrise, not the colour of the sky.
✗ Reflection — reflection would simply return sunlight unchanged; it cannot separate the colours of white light.
✗ Total internal reflection — this occurs when light goes from a denser to a rarer medium beyond the critical angle; it explains optical fibres, mirages and the sparkle of a diamond.
📌 SSC & Railway Exam Facts
• Rayleigh scattering ∝ 1/λ⁴ — shorter wavelength means stronger scattering.
• Danger signals are red because red has the longest wavelength and is scattered the least, so it is seen from far away.
• Tyndall effect is the scattering of light by a colloid, which makes the beam path visible.
• Clouds look white because large water droplets scatter all wavelengths equally.
• Sequence of visible spectrum: VIBGYOR; violet has the least wavelength, red the most.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q66. What is the cause of the apparent elevation of a star's position when viewed near the horizon?

  1. (a) The gravitational force of Earth on starlight
  2. (b) Atmospheric absorption of starlight
  3. (c) Atmospheric refraction of starlight towards the normal
  4. (d) Reflection of starlight away from the normal
Answer & solution

Answer: (c) Atmospheric refraction of starlight towards the normal

Correct Answer: Option 3 — Atmospheric refraction of starlight towards the normal
The Earth's atmosphere is not uniform — its density, and therefore its refractive index, increases steadily as we come down towards the surface. So starlight entering the atmosphere travels continuously from an optically rarer to an optically denser medium.
Whenever light goes from a rarer to a denser medium it bends towards the normal. Because the change is gradual, the ray follows a slightly curved path and bends a little more at every layer.
We always see a star along the straight line in which the light finally enters the eye. That final direction is tilted, so the star appears to be higher up (elevated) than its true position. The effect is largest near the horizon, where the light has to cross the greatest thickness of atmosphere.
The same effect makes the Sun visible about 2 minutes before actual sunrise and about 2 minutes after actual sunset.
❌ Why the other options are incorrect
✗ The gravitational force of Earth on starlight — the bending of light by the Earth's gravity is far too small to be noticed; it is a general-relativity effect seen only near very massive bodies like the Sun.
✗ Atmospheric absorption of starlight — absorption only makes the star look fainter; it cannot shift its apparent position.
✗ Reflection of starlight away from the normal — reflection sends light back into the same medium and in any case reflection cannot bend light away from the normal in this sense; the phenomenon here is refraction.
📌 SSC & Railway Exam Facts
• Rarer to denser → bends towards the normal; denser to rarer → bends away from the normal.
• Atmospheric refraction causes the twinkling of stars, the advanced sunrise and delayed sunset, and the oval-shaped Sun at the horizon.
• The day is lengthened by about 4 minutes in total because of atmospheric refraction.
• Refractive index of air ≈ 1.0003; n = c/v, with c = 3 × 10⁸ m/s.
• Stars twinkle but planets do not, because planets subtend a larger angle at the eye.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 2 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q67. The twinkling of stars is due to ___________.

  1. (a) the atmospheric refraction of light from the star
  2. (b) the atmospheric reflection of light from the stars
  3. (c) the interference of light from different stars
  4. (d) the interference of light from a star and moon
Answer & solution

Answer: (a) the atmospheric refraction of light from the star

Correct Answer: Option 1 — the atmospheric refraction of light from the star
The twinkling of stars is caused by atmospheric refraction of starlight. The earth's atmosphere is made of layers of different optical densities, and these layers keep changing because of wind and temperature variations.
Starlight entering the atmosphere therefore bends continuously and, since a star is practically a point source, its apparent position and the amount of light reaching the eye keep fluctuating. The star thus appears to twinkle — sometimes bright, sometimes dim.
Planets do not twinkle because a planet is much closer and acts as a collection of point sources (an extended source). The variations in light from the different points average out, so the total light reaching the eye stays steady.
❌ Why the other options are incorrect
✗ the atmospheric reflection of light from the stars — reflection sends light back from a surface; the atmosphere transmits and bends starlight, it does not reflect it back.
✗ the interference of light from different stars — stars are independent, incoherent sources, so light from two stars cannot produce a steady interference pattern.
✗ the interference of light from a star and moon — the moon only reflects sunlight; it is again incoherent with starlight and cannot cause twinkling.
📌 SSC & Railway Exam Facts
• Stars twinkle, planets do not — a classic one-mark question.
• Atmospheric refraction also causes the advanced sunrise and delayed sunset by about 2 minutes each.
• The sun appears flattened (oval) at sunrise and sunset due to refraction.
• Scattering of light by the atmosphere makes the sky blue and the setting sun red.
• The Tyndall effect is the scattering of light by colloidal particles.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 2 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q68. The apparent position of a star keeps on changing slightly because:

  1. (a) Different layers of the atmosphere have different density
  2. (b) Star doesn't have it's own light
  3. (c) Different layers of the atmosphere are of same density
  4. (d) Stars are very close to the surface of the earth.
Answer & solution

Answer: (a) Different layers of the atmosphere have different density

Correct Answer: Option 1 — Different layers of the atmosphere have different density
The earth's atmosphere is not uniform. Its layers have different densities, and therefore different refractive indices, which go on changing with wind, pressure and temperature.
When starlight travels down through this uneven atmosphere it is refracted again and again, bending a little more each time towards the normal as it enters denser air. Because the refracting layers keep shifting, the direction in which the light finally reaches the eye also keeps shifting. The star therefore appears slightly displaced from its true position, and that apparent position keeps changing — which is also why the star seems to twinkle.
For the same reason a star near the horizon appears higher than it really is, and the sun is visible about 2 minutes before actual sunrise and 2 minutes after actual sunset.
❌ Why the other options are incorrect
✗ Star doesn't have it's own light — false in fact; a star is a self-luminous body that produces its own light by nuclear fusion. It is the moon and planets that shine by reflected light.
✗ Different layers of the atmosphere are of same density — if the density were the same everywhere there would be no refraction at all, and the star's position would never shift.
✗ Stars are very close to the surface of the earth — stars are extremely far away; the nearest star after the sun, Proxima Centauri, is about 4.2 light years away.
📌 SSC & Railway Exam Facts
• Atmospheric refraction explains twinkling of stars, advanced sunrise and delayed sunset.
• Planets do not twinkle because they are extended sources, not point sources.
• Refractive index n = c/v; light bends towards the normal on entering a denser medium.
• The sun looks oval and red at sunrise and sunset due to refraction and scattering.
• The apparent flattening of the sun's disc is also an effect of atmospheric refraction.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 2 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q69. The most scattered colour of the sun light when it enters the earth's atmosphere is _______.

  1. (a) green
  2. (b) pink
  3. (c) red
  4. (d) blue
Answer & solution

Answer: (d) blue

Correct Answer: Option 4 — blue
When sunlight enters the earth's atmosphere it strikes molecules of air that are much smaller than the wavelength of visible light. Such tiny particles scatter light according to Rayleigh's law of scattering:
Amount of scattering ∝ 1/λ⁴
Since scattering is inversely proportional to the fourth power of the wavelength, the shorter wavelengths are scattered far more strongly. In the visible spectrum violet and blue have the shortest wavelengths, so they are scattered the most; red, with the longest wavelength, is scattered the least.
The eye is less sensitive to violet than to blue, and part of the violet is absorbed high in the atmosphere — so the scattered light we finally see makes the sky look blue.
❌ Why the other options are incorrect
✗ green — green lies in the middle of the visible spectrum (about 550 nm), so it is scattered less than blue.
✗ pink — pink is not a spectral colour of white light at all; it is a mixture, and does not appear in the VIBGYOR sequence.
✗ red — red has the longest wavelength (about 700 nm), so it is least scattered; that is why red is used for danger signals and why the setting sun looks red.
📌 SSC & Railway Exam Facts
• Rayleigh scattering: intensity ∝ 1/λ⁴ — shorter wavelength scatters more.
• Wavelength order VIBGYOR: violet shortest (≈ 400 nm), red longest (≈ 700 nm).
• Red light travels the farthest through fog, so danger signals are red.
• The sky looks black to an astronaut because there is no atmosphere to scatter light in space.
• The sun looks red at sunrise and sunset because blue light is scattered away over the long slant path.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 1 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q70. Which phenomenon is responsible for the twinkling of a star?

  1. (a) Scattering
  2. (b) Reflection
  3. (c) Total internal reflection
  4. (d) Atmospheric refraction
Answer & solution

Answer: (d) Atmospheric refraction

Correct Answer: Option 4 — Atmospheric refraction
The twinkling (scintillation) of stars is caused by atmospheric refraction. The earth's atmosphere is not uniform: its density and hence its refractive index keep changing with height and with time as air layers move. Starlight entering this restless atmosphere is refracted continuously, and because a star is so far away it acts as a point source. So the apparent position of the star goes on shifting slightly, and the amount of light reaching the eye keeps varying — the star appears to twinkle.
Planets do not twinkle. A planet is much nearer and behaves as a collection of a large number of point sources; the variations from all those points average out, giving a steady light. Atmospheric refraction also makes the Sun appear about 2 minutes earlier at sunrise and 2 minutes later at sunset, and makes stars appear a little higher than they really are.
❌ Why the other options are incorrect
✗ Scattering — scattering of light by air molecules explains the blue sky, the red sun at sunrise and sunset and the Tyndall effect, not twinkling.
✗ Reflection — bouncing back of light from a surface; it produces images in mirrors and does not occur in the open atmosphere in this way.
✗ Total internal reflection — happens only when light goes from a denser to a rarer medium beyond the critical angle; it explains optical fibres, mirages and the sparkle of a diamond.
📌 SSC & Railway Exam Facts
• Twinkling of stars, advance sunrise and delayed sunset → atmospheric refraction.
• Blue colour of the sky, red sun at sunrise/sunset, white clouds → scattering of light.
• Rayleigh scattering: amount of scattering ∝ 1/λ⁴ — blue scatters most, red least.
• Mirage and optical fibre → total internal reflection; rainbow → refraction + dispersion + total internal reflection in raindrops.
• Stars twinkle but planets do not, because planets are extended sources.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 2 · Defects of vision and their correction

Q71. Select the correct pair from the following options based on the refractive defects of vision.

  1. (a) (a) Hypermetropia - near-sightedness (b) Presbyopia - far-sightedness
  2. (b) (a) Presbyopia - near-sightedness (b) Myopia - far-sightedness
  3. (c) (a) Presbyopia - near-sightedness (b) Hypermetropia - far-sightedness
  4. (d) (a) Myopia - near-sightedness (b) Hypermetropia - far-sightedness
Answer & solution

Answer: (d) (a) Myopia - near-sightedness (b) Hypermetropia - far-sightedness

Correct Answer: Option 4 — (a) Myopia - near-sightedness, (b) Hypermetropia - far-sightedness
Myopia is also called near-sightedness or short-sightedness. Such an eye can see nearby objects clearly but distant objects appear blurred, because the image of a distant object forms in front of the retina. It happens when the eyeball is too long or the curvature of the lens is too great. It is corrected with a concave (diverging) lens of suitable power.
Hypermetropia is also called far-sightedness or long-sightedness. Such an eye can see distant objects clearly but nearby objects appear blurred, because the image of a near object forms behind the retina. It happens when the eyeball is too short or the focal length of the lens is too long, and it is corrected with a convex (converging) lens.
❌ Why the other options are incorrect
✗ Option 1 — Hypermetropia is far-sightedness, not near-sightedness, so pair (a) is wrong.
✗ Option 2 — Myopia is near-sightedness, not far-sightedness, so pair (b) is wrong.
✗ Option 3 — Presbyopia is the old-age defect of losing the power of accommodation; calling it near-sightedness is wrong.
📌 SSC & Railway Exam Facts
• Myopia → concave lens; Hypermetropia → convex lens; Presbyopia → bifocal lens.
• Normal near point = 25 cm and far point = infinity for a healthy eye.
• Astigmatism is corrected by a cylindrical lens.
• Power of a lens P = 1/f (in metres), SI unit dioptre (D).
• Cataract is the clouding of the eye lens; it is cured by surgery, not by spectacles.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 3 · Prism and dispersion of light

Q72. When a white light falls on a glass prism, ________ colour undergoes maximum deviation.

  1. (a) Violet
  2. (b) Blue
  3. (c) Yellow
  4. (d) Red
Answer & solution

Answer: (a) Violet

Correct Answer: Option 1 — Violet
When white light passes through a glass prism it splits into seven colours — VIBGYOR. This splitting is called dispersion of light, first explained by Isaac Newton.
Dispersion happens because the refractive index of glass is different for different colours. Violet light has the shortest wavelength, and for it the refractive index of glass is the highest. A higher refractive index means the ray bends more, so violet is deviated the most.
Red light has the longest wavelength and the lowest refractive index in glass, so it bends the least. That is why on the screen violet appears at the bottom of the spectrum and red at the top.
❌ Why the other options are incorrect
✗ Blue — blue is deviated a lot, but still less than violet, because its wavelength is longer than violet's.
✗ Yellow — yellow lies in the middle of the spectrum and suffers only a moderate deviation.
✗ Red — red suffers the least deviation of all seven colours, the exact opposite of what is asked.
📌 SSC & Railway Exam Facts
• Order of deviation: Violet > Indigo > Blue > Green > Yellow > Orange > Red.
• Order of wavelength is the reverse: Red (≈ 700 nm) > … > Violet (≈ 400 nm).
• Dispersion was explained by Isaac Newton, who recombined the colours with a second prism.
• A rainbow is formed by refraction, total internal reflection and dispersion in water droplets.
• The sky is blue because of the scattering of light (Rayleigh scattering), not dispersion.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 1 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q73. The phenomenon of scattering of light by the colloidal particles gives rise to:

  1. (a) Tyndall effect
  2. (b) delay in sunset
  3. (c) rainbow
  4. (d) twinkling of stars
Answer & solution

Answer: (a) Tyndall effect

Correct Answer: Option 1 — Tyndall effect
When a beam of light passes through a colloid — a medium containing extremely fine suspended particles such as smoke, fog, mist or a dusty room — the particles scatter the light sideways. As a result the path of the beam itself becomes visible. This phenomenon is called the Tyndall effect, named after the British scientist John Tyndall.
Everyday examples are a beam of sunlight entering a dark room through a small hole, the visible beam of a cinema projector in a smoky hall, and the headlight beams of a car in fog. The Tyndall effect is also used to distinguish a colloid from a true solution — a true solution, whose particles are far too small, shows no Tyndall effect.
❌ Why the other options are incorrect
✗ delay in sunset — the Sun stays visible for a few minutes after it has actually set because of atmospheric refraction, not scattering.
✗ rainbow — a rainbow is formed inside raindrops by refraction, total internal reflection and dispersion of sunlight, not by scattering off colloidal particles.
✗ twinkling of stars — stars twinkle because of the refraction of starlight through air layers of continuously changing density.
📌 SSC & Railway Exam Facts
• Tyndall effect — scattering of light by colloidal particles, which makes the path of a light beam visible.
• The blue colour of the sky is due to scattering; blue light, having a shorter wavelength, is scattered the most.
• Rayleigh's law: intensity of scattering ∝ 1/λ⁴.
• The Sun looks reddish at sunrise and sunset because blue light is scattered away over the long path through the atmosphere.
• Danger signals are red — red has the longest wavelength and is scattered the least, so it travels farthest.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 1 · Prism and dispersion of light

Q74. What is the name of the phenomenon that causes white light to split into seven colours as it passes through a glass prism?

  1. (a) Dispersion
  2. (b) Refraction
  3. (c) Diffraction
  4. (d) Scattering
Answer & solution

Answer: (a) Dispersion

Correct Answer: Option 1 — Dispersion
The splitting of white light into its seven constituent colours on passing through a glass prism is called dispersion of light. It was first demonstrated by Sir Isaac Newton. The band of colours obtained is called the spectrum, and the order from the least to the most deviated is 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, so glass bends it the most, while red has the longest wavelength and is bent the least. A second, inverted prism can recombine these colours back into white light.
❌ Why the other options are incorrect
✗ Refraction — refraction is simply the bending of light when it enters a new medium; it is the *cause* of dispersion, but by itself it does not split white light into colours.
✗ Diffraction — diffraction is the bending of light around an obstacle or through a narrow slit, comparable in size to the wavelength; it is a different phenomenon from prism dispersion.
✗ Scattering — scattering is the spreading of light by fine particles; it explains the blue sky and the Tyndall effect, not the prism spectrum.
📌 SSC & Railway Exam Facts
• Dispersion through a prism was first shown by Sir Isaac Newton; the coloured band is the spectrum.
• Order of colours: VIBGYOR; violet deviates the most, red the least.
• Wavelength order is the reverse — red (≈ 700 nm) > ... > violet (≈ 400 nm).
• A rainbow is nature's prism — formed by refraction, total internal reflection and dispersion in raindrops.
• The blue sky and the red Sun at sunset are due to scattering, while twinkling of stars is due to atmospheric refraction.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 3 · Defects of vision and their correction

Q75. Which of the following symptoms is related to myopia?

  1. (a) A person can see both nearby and distant objects distinctly.
  2. (b) A person cannot see both nearby and distant objects distinctly.
  3. (c) A person can see distant objects clearly but cannot see nearby objects distinctly.
  4. (d) A person can see nearby objects clearly but cannot see distant objects distinctly.
Answer & solution

Answer: (d) A person can see nearby objects clearly but cannot see distant objects distinctly.

Correct Answer: Option 4 — A person can see nearby objects clearly but cannot see distant objects distinctly.
Myopia, or short-sightedness (near-sightedness), is the defect in which a person can see near objects clearly but distant objects appear blurred. It happens because the image of a distant object is formed in front of the retina instead of on it. The two usual causes are excessive curvature of the eye lens (too much converging power) or an elongated eyeball.
In myopia the far point shifts from infinity to some finite distance. The defect is corrected by using a concave (diverging) lens of suitable negative power, which first diverges the incoming parallel rays a little so that the eye lens can then bring them to focus exactly on the retina.
❌ Why the other options are incorrect
✗ A person can see both nearby and distant objects distinctly. — this describes a normal, defect-free eye, not myopia.
✗ A person cannot see both nearby and distant objects distinctly. — this fits presbyopia in old age, where both near and far vision weaken and bifocal lenses are used.
✗ A person can see distant objects clearly but cannot see nearby objects distinctly. — this is the exact opposite defect, hypermetropia (long-sightedness), corrected with a convex lens.
📌 SSC & Railway Exam Facts
• Myopia — concave lens, power is negative; far point comes nearer than infinity.
• Hypermetropia — convex lens, power is positive; near point moves beyond 25 cm.
• Presbyopia — corrected by bifocal lenses; astigmatism — corrected by a cylindrical lens.
• Least distance of distinct vision for a normal eye = 25 cm; far point = infinity.
• The eye focuses by changing the focal length of the eye lens — this is called accommodation, done by the ciliary muscles.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 1 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q76. The phenomenon of scattering of light by the colloidal particles gives rise to:

  1. (a) rainbow
  2. (b) twinkling of stars
  3. (c) delay in sunset
  4. (d) Tyndall effect
Answer & solution

Answer: (d) Tyndall effect

Correct Answer: Option 4 — Tyndall effect
When a beam of light passes through a medium containing colloidal particles — particles large enough to scatter light but too small to be seen — the light is scattered and the path of the beam becomes visible. This phenomenon is called the Tyndall effect, named after the scientist John Tyndall.
Familiar examples are a beam of sunlight entering a dark room through a small hole, which reveals the dust particles floating in the air, and the beam of a torch or a cinema projector seen in smoke or mist.
Scattering also explains many everyday sights: the sky looks blue because the tiny molecules of air scatter the shorter blue wavelengths most (Rayleigh scattering, scattering ∝ 1/λ⁴), and the Sun looks red at sunrise and sunset because the blue light has been scattered away over the long slanting path, leaving the red to reach our eyes.
❌ Why the other options are incorrect
✗ rainbow — a rainbow is formed by refraction, total internal reflection and dispersion of sunlight inside water droplets, not by scattering.
✗ twinkling of stars — this is caused by atmospheric refraction, because the starlight keeps bending through air layers of changing density.
✗ delay in sunset — the apparent advance sunrise and delayed sunset are also effects of atmospheric refraction, not of scattering.
📌 SSC & Railway Exam Facts
• Tyndall effect is used to distinguish a colloid from a true solution — a true solution shows no visible beam.
• Rayleigh's law: amount of scattering ∝ 1/λ⁴, so blue (shorter λ) scatters more than red.
• Danger signals and traffic stop lights are red because red has the longest wavelength and is scattered the least, so it is visible from far away.
• The sky appears black to an astronaut because there is no atmosphere in space to scatter light.
• Clouds appear white because their large water droplets scatter all wavelengths almost equally.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 2 · Prism and dispersion of light

Q77. Among all the seven-coloured lights, which colour deviates the most after falling on a prism?

  1. (a) Violet
  2. (b) Red
  3. (c) Yellow
  4. (d) Indigo
Answer & solution

Answer: (a) Violet

Correct Answer: Option 1 — Violet
When white light passes through a glass prism it splits into seven colours — this is called dispersion. The colours appear in the order VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red) from the bottom of the spectrum upward.
The amount of bending depends on the wavelength of the colour. Violet has the shortest wavelength (about 400 nm), so the glass has the highest refractive index for it and it bends (deviates) the most. Red has the longest wavelength (about 700 nm), the lowest refractive index, and therefore deviates the least.
❌ Why the other options are incorrect
✗ Red — it has the longest wavelength in the visible spectrum, so it is bent the least by the prism, not the most.
✗ Yellow — its wavelength lies in the middle of the spectrum, so its deviation is only moderate.
✗ Indigo — it deviates a great deal, but still less than violet, because its wavelength is slightly longer than violet's.
📌 SSC & Railway Exam Facts
• Dispersion of light through a prism was first demonstrated by Sir Isaac Newton.
• The band of seven colours produced is called the spectrum; the sequence is VIBGYOR.
• Order of deviation: Violet > Indigo > Blue > Green > Yellow > Orange > Red.
• Order of wavelength is exactly the reverse: Red > Orange > Yellow > Green > Blue > Indigo > Violet.
• A rainbow is formed by refraction, total internal reflection and dispersion of sunlight in raindrops.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 3 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q78. What determines the colour of scattered light in the Tyndall effect?

  1. (a) The angle of refraction of the emerging light.
  2. (b) The size of the scattering particles.
  3. (c) The angle of incidence of the incoming light.
  4. (d) The distance between the source of light and the scattering particles.
Answer & solution

Answer: (b) The size of the scattering particles.

Correct Answer: Option 2 — The size of the scattering particles.
When a beam of light passes through a medium containing fine suspended particles — smoke, fog, dust or a colloid — the particles scatter the light sideways and the path of the beam becomes visible. This is the Tyndall effect, named after the British scientist John Tyndall.
The colour that is scattered most depends on the size of the scattering particles compared with the wavelength of light. Very fine particles scatter mainly blue (short-wavelength) light, which is why the sky looks blue; larger particles scatter all wavelengths almost equally, so the scattered light looks white, as in clouds, mist and fog. By Rayleigh's law the intensity of scattering is ∝ 1/λ⁴.
❌ Why the other options are incorrect
✗ The angle of refraction of the emerging light — refraction is the bending of light as it enters a new medium; scattering is a different phenomenon, and the colour scattered does not depend on this angle.
✗ The angle of incidence of the incoming light — changing the angle of incidence changes the direction of the beam, not the colour of the light scattered.
✗ The distance between the source of light and the scattering particles — a greater distance only makes the beam fainter; the colour of the scattered light stays the same.
📌 SSC & Railway Exam Facts
• Tyndall effect — scattering of light by colloidal particles that makes the path of a beam visible.
• The blue colour of the sky and the red colour of the Sun at sunrise and sunset are both due to scattering.
• Rayleigh scattering: intensity ∝ 1/λ⁴ — blue light is scattered about 16 times more than red.
• Danger signals are red because red has the longest wavelength and is scattered the least, so it is seen from far away.
• Outside the atmosphere there is nothing to scatter light, so the sky appears black to an astronaut.
RRB Technician Grade III 2024-25 – 20 December 2024 Shift 2 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q79. Which of the following events is a consequence of atmospheric refraction?

  1. (a) Curved mirrors to form enlarged image of an object
  2. (b) Advance sunrise and delayed sunset
  3. (c) Rainbow formation
  4. (d) Image formation by plain mirrors
Answer & solution

Answer: (b) Advance sunrise and delayed sunset

Correct Answer: Option 2 — Advance sunrise and delayed sunset
Atmospheric refraction is the bending of light as it passes through layers of air of continuously changing optical density. Air near the ground is denser (hotter and more compressed) than air higher up, so a ray coming from the Sun bends towards the normal as it enters denser layers and follows a curved path.
Because of this, the Sun is seen about 2 minutes before it actually rises above the horizon and continues to be seen about 2 minutes after it has actually set — giving an advanced sunrise and a delayed sunset, and lengthening the day by roughly 4 minutes. The twinkling of stars, the apparent flattening of the Sun's disc at sunrise/sunset and the advance apparent position of the Sun are all effects of the same phenomenon.
❌ Why the other options are incorrect
✗ Curved mirrors to form enlarged image of an object — this is reflection by a concave mirror, not refraction.
✗ Rainbow formation — caused by refraction, total internal reflection and dispersion of sunlight inside water droplets, not by the atmosphere's density layers.
✗ Image formation by plain mirrors — plane mirrors work purely by the laws of reflection; the image is virtual, erect and of the same size.
📌 SSC & Railway Exam Facts
• The day appears about 4 minutes longer because of atmospheric refraction.
• Twinkling of stars (stellar scintillation) is due to atmospheric refraction; planets do not twinkle because they are extended sources.
• The blue colour of the sky and the red colour of the rising/setting Sun are due to scattering, not refraction.
• Refractive index of air ≈ 1.0003; of water 1.33, of glass about 1.5, of diamond 2.42.
RRB Technician Grade III 2024-25 – 20 December 2024 Shift 2 · Prism and dispersion of light

Q80. What is the angle between the two lateral faces of a triangular glass prism called?

  1. (a) Inclination angle
  2. (b) Base angle
  3. (c) Angle of prism
  4. (d) Angle of deviation
Answer & solution

Answer: (c) Angle of prism

Correct Answer: Option 3 — Angle of prism
A glass prism is a transparent refracting medium bounded by two triangular bases and three rectangular lateral surfaces. The angle between its two refracting (lateral) faces on which light is incident and from which it emerges is called the angle of prism or the refracting angle, usually denoted by A. For the common equilateral prism used in the laboratory, A = 60°.
When a ray of white light passes through a prism it bends towards the base at both surfaces, and the angle between the direction of the incident ray and the emergent ray is the angle of deviation (D). Different colours are deviated by different amounts, which splits white light into its seven colours — the phenomenon of dispersion, first demonstrated by Sir Isaac Newton.
❌ Why the other options are incorrect
✗ Inclination angle — a general geometry term for the tilt of a line or plane; it is not used for the refracting angle of a prism.
✗ Base angle — the angle a lateral face makes with the base of the triangular face; light does not refract using this angle.
✗ Angle of deviation — the angle between the incident ray produced forward and the emergent ray; it is a property of the ray path, not of the prism's geometry alone.
📌 SSC & Railway Exam Facts
• Prism relation: A + D = i + e, where i is the angle of incidence and e the angle of emergence.
• At minimum deviation, i = e and the refracted ray inside the prism is parallel to the base.
• μ = sin[(A + D(m))/2] / sin(A/2) is the prism formula for refractive index.
• VIBGYOR — violet deviates the most, red the least, because violet has the shortest wavelength.
• Newton used a prism to obtain the spectrum and a second, inverted prism to recombine it into white light.
RRB JE CBT-1 2024-25 – 18 December 2024 Shift 2 · Atmospheric refraction (twinkling of stars, advance sunrise)

Q81. Why do stars appear to twinkle when viewed from the Earth?

  1. (a) Scattering by particles
  2. (b) Diffraction by clouds
  3. (c) Reflection in the atmosphere
  4. (d) Refraction in the Earth’s atmosphere
Answer & solution

Answer: (d) Refraction in the Earth’s atmosphere

Answer: Option 4 — Refraction in the Earth's atmosphere
Starlight passes through air layers whose temperature and density keep changing, so its refraction keeps changing.
The apparent position and brightness of the star flicker — this is twinkling, due to atmospheric refraction.
Revision note — Atmospheric refraction
• Hotter air is optically rarer, cooler air optically denser — light bends as it crosses them.
• A star is a point source very far away, so a small change in its light path is noticeable.
• Planets do not twinkle — they are much nearer, act as extended sources (many point sources), and the flickers average out.
• A star appears slightly higher than its actual position when seen near the horizon.
• Advance sunrise and delayed sunset — the Sun is seen about 2 minutes before actual sunrise and after actual sunset.
• The Sun's disc looks flattened at sunrise and sunset for the same reason.
Do not mix these up
• Refraction vs scattering — twinkling and advance sunrise are refraction; blue sky, red sunset and the Tyndall effect are scattering.
Also asked from this topic: why the Sun's disc looks flattened at sunrise and sunset (atmospheric refraction); the cause of a mirage on a hot road (refraction through hot air layers).
RRB JE CBT-1 2024-25 – 18 December 2024 Shift 3 · Prism and dispersion of light

Q82. What is the term for the band of colours produced when light is dispersed?

  1. (a) Reflection
  2. (b) Refraction
  3. (c) Absorption
  4. (d) Spectrum
Answer & solution

Answer: (d) Spectrum

Answer: Option 4 — Spectrum
When white light splits into its colours (dispersion), the band of colours formed is called the spectrum — VIBGYOR.
Revision note — Dispersion of light
• Dispersion — splitting of white light into its component colours by a glass prism.
• Cause — each colour has a different wavelength, so it bends by a different amount in glass.
• Violet bends the most, red the least; red has the longest wavelength.
• Isaac Newton first obtained the spectrum of sunlight with a prism (1666).
• An inverted second prism recombines the colours into white light.
• A rainbow forms by refraction, dispersion and internal reflection in raindrops; it is seen with the Sun behind the observer.
Do not mix these up
• Dispersion vs spectrum — dispersion is the process; the spectrum is the band of colours it produces.
• Dispersion vs scattering — dispersion gives the rainbow; scattering gives the blue sky and red sunset.
Also asked from this topic: cause of spectrum formation by a prism (dispersion); who first explained dispersion (Isaac Newton); effect of an inverted second prism (recombines into white light).
RRB JE CBT-1 2024-25 – 17 December 2024 Shift 1 · Scattering of light (blue sky, red sunset, Tyndall effect)

Q83. Why are danger signals typically red in colour?

  1. (a) Red light is more reflective than other colours.
  2. (b) The colour red is aesthetically pleasing.
  3. (c) Red light is easier to produce artificially.
  4. (d) Red light has a longer wavelength and is scattered the least, making it visible from a distance.
Answer & solution

Answer: (d) Red light has a longer wavelength and is scattered the least, making it visible from a distance.

Answer: Option 4 — Red light has a longer wavelength and is scattered the least, making it visible from a distance.
Tiny particles scatter short wavelengths much more than long ones.
Red has the longest wavelength of visible light, so it passes through fog and smoke with the least scattering.
Revision note — Scattering of light
• Rayleigh scattering: intensity ∝ 1/λ^(4) — halve the wavelength and scattering rises 16 times.
• Visible order by wavelength: VIBGYOR — violet is shortest (about 400 nm), red is longest (about 700 nm).
• Blue sky — air molecules scatter blue light more than red.
• Red sun at sunrise and sunset — light crosses a thicker layer of air, blue is scattered away, red reaches the eye.
• Sky looks black to astronauts in space — no atmosphere to scatter light.
• Tyndall effect — scattering of light by colloidal particles, e.g. a sunbeam in a dusty room.
• Very large particles (clouds) scatter all colours equally, so clouds look white.
Also asked from this topic: why the sky looks blue in the daytime (blue, shorter wavelength, is scattered more); how particle size affects scattering (smaller particles scatter shorter wavelengths more).
RRB JE CBT-1 2024-25 – 17 December 2024 Shift 3 · Prism and dispersion of light

Q84. What is the angle formed between two lateral faces of a triangular glass prism called?

  1. (a) Angle of incidence
  2. (b) Angle of deviation
  3. (c) Angle of refraction
  4. (d) Angle of the prism
Answer & solution

Answer: (d) Angle of the prism

Answer: Option 4 — Angle of the prism
A triangular glass prism has two triangular bases and three rectangular lateral faces.
The angle between the two lateral faces through which light enters and leaves is the angle of the prism (refracting angle).
Revision note — Refraction through a glass prism
• The angle between the incident ray and the emergent ray is the angle of deviation.
• Light bends towards the base of the prism after passing through it.
• White light splits into seven colours (VIBGYOR) — dispersion; the band of colours is a spectrum.
• Violet bends the most, red the least, because each colour has a different speed (refractive index) in glass.
• Isaac Newton first used a glass prism to obtain the spectrum of sunlight; a second inverted prism recombines the colours into white light.
• A rainbow is a natural spectrum formed by water droplets acting like tiny prisms.
Do not mix these up
• Angle of the prism vs angle of deviation — the first is between the two faces (a property of the prism); the second is between incident and emergent rays.
Also asked from this topic: the angle between incident and emergent rays (angle of deviation); formation of a spectrum by a prism (dispersion); who first explained the dispersion of white light (Isaac Newton).
RRB JE CBT-1 2024-25 – 16 December 2024 Shift 3 · Prism and dispersion of light

Q85. When light exits a prism, what is the result of its interaction with the prism surfaces?

  1. (a) Light passes through without any change.
  2. (b) Light is only reflected.
  3. (c) Light is only absorbed.
  4. (d) Light is refracted.
Answer & solution

Answer: (d) Light is refracted.

Answer: Option 4 — Light is refracted.
Light bends (refracts) as it enters the prism and again as it leaves it.
The two faces are inclined, so the bends add up and the ray is deviated towards the base.
Revision note — Refraction through a glass prism
• At the first face light goes from air to glass and bends towards the normal.
• At the second face it goes from glass to air and bends away from the normal.
• Angle of deviation — angle between the incident ray produced and the emergent ray.
• Angle of the prism — angle between the two refracting faces (commonly 60°).
• Dispersion — white light splits into VIBGYOR; violet deviates most, red least.
• A second, inverted prism recombines the colours into white light (Newton).
Do not mix these up
• Glass slab vs prism — a slab's faces are parallel, so the emergent ray is parallel to the incident ray (only shifted); a prism's are inclined, so the ray is deviated.
Also asked from this topic: where the ray bends inside a prism (towards the base); why the emergent ray is not parallel (inclined refracting faces); splitting of white light (dispersion).

More Physics chapters

Work, Energy and Power196 questionsElectricity187 questionsMagnetism and Magnetic Effects of Current129 questionsMotion123 questionsSound and Waves123 questionsForce and Laws of Motion112 questionsLight - Reflection and Mirrors106 questionsLight - Refraction and Lenses103 questionsGravitation90 questionsUnits, Measurement & Dimensions56 questionsHeat and Thermodynamics47 questionsSources of Energy38 questionsPhysics Miscellaneous33 questionsPressure, Fluids and Properties of Matter30 questionsModern Physics and Electronics24 questions
📥 PDF of this paper (all subjects, English & Hindi): All previous year papers PDF · ▶ Attempt previous year papers as free online tests · 🏆 Free live mock tests · 📰 Daily current affairs quiz