Q1. The refractive index represents which of the following?
a) Mass of a medium
b) Change in direction of a ray in a medium
c) Colour of light
d) Temperature of medium
Answer: Change in direction of a ray in a medium.
Why correct: Refractive index measures how much a medium bends (refracts) light when it enters from another medium.
Why others wrong:
a) Mass of medium has no relation to refraction; optical density ≠ mass density.
c) Colour does not determine refractive index.
d) Temperature does not define refractive index in this context.
Q2. Light travels fastest in which medium?
a) Water
b) Glass
c) Vacuum
d) Alcohol
Answer: Vacuum.
Why correct: Light achieves its maximum possible speed (3 × 10⁸ m/s) in vacuum.
Why others wrong:
a) Water slows light compared to air or vacuum.
b) Glass is denser and slows light even more.
d) Alcohol also reduces the speed of light.
Q3. The speed of light in vacuum is approximately:
a) 3 × 10⁵ m/s
b) 3 × 10⁶ m/s
c) 3 × 10⁸ m/s
d) 3 × 10¹⁰ m/s
Answer: 3 × 10⁸ m/s.
Why correct: This is the universally accepted speed of light in vacuum.
Why others wrong:
a) and b) are too low.
d) is too high.
Q4. When light travels from one medium to another, its:
a) Frequency changes
b) Colour changes
c) Direction may change
d) Wavelength remains constant
Answer: Direction may change.
Why correct: Change in speed at the boundary causes bending of light, altering its direction.
Why others wrong:
a) Frequency remains constant in refraction.
b) Colour (linked to frequency) also stays the same.
d) Wavelength does change, not remain constant.
Q5. Refractive index of a medium depends on:
a) Temperature
b) Speed of light in two media
c) Mass of medium
d) Optical instruments
Answer: Speed of light in two media.
Why correct: Refractive index is defined as the ratio of light’s speed in two media (n = V₁/V₂).
Why others wrong:
a) Temperature may affect refractive index but is not the defining factor.
c) Mass has no direct relation to optical density.
d) Instruments do not determine refractive index.
Q6. The refractive index of medium 2 with respect to medium 1 is represented by:
a) n₁₂
b) n₂₁
c) n₁
d) n₂
Answer: n₂₁.
Why correct: n₂₁ means refractive index of medium 2 relative to medium 1.
Why others wrong:
a) n₁₂ is the opposite ratio.
c) n₁ and d) n₂ represent individual media, not comparison.
Q7. If V₁ and V₂ are speeds of light in media 1 and 2 respectively, then n₂₁ =
a) V₂ / V₁
b) V₁ × V₂
c) V₁ / V₂
d) 1/(V₁V₂)
Answer: V₁ / V₂.
Why correct: Refractive index = speed in medium 1 ÷ speed in medium 2.
Why others wrong:
a) Gives inverse refractive index.
b) and d) are not meaningful in optics.
Q8. The absolute refractive index is taken with respect to:
a) Water
b) Air
c) Alcohol
d) Rock salt
Answer: Air.
Why correct: Absolute refractive index means refractive index relative to vacuum/air.
Why others wrong:
a, c, d) These are media being measured, not the reference medium.
Q9. If c is the speed of light in air and v in a medium, refractive index is:
a) v/c
b) c/v
c) c × v
d) 1/(cv)
Answer: c/v.
Why correct: n = speed in air ÷ speed in medium = c/v.
Why others wrong:
a) v/c gives inverse.
c) and d) do not express any physical refraction property.
Q10. Refractive index of water is approximately:
a) 1.00
b) 1.31
c) 1.33
d) 1.77
Answer: 1.33.
Why correct: Standard value from the given table.
Why others wrong:
a) Slightly above 1, but too low.
b) 1.31 corresponds to ice.
d) 1.77 corresponds to sapphire.
Q11. Which medium has a refractive index around 1.52?
a) Ice
b) Turpentine oil
c) Crown glass
d) Alcohol
Answer: Crown glass.
Why correct: The table clearly lists crown glass with refractive index 1.52.
Why others wrong:
a) Ice ≈ 1.31
b) Turpentine oil ≈ 1.47
d) Alcohol ≈ 1.36
Q12. The medium with the highest refractive index in the table is:
a) Sapphire
b) Dense flint glass
c) Diamond
d) Carbon disulphide
Answer: Diamond.
Why correct: Diamond has the highest value listed: 2.42.
Why others wrong:
a) Sapphire: 1.77
b) Dense flint glass: 1.65
d) Carbon disulphide: 1.63
Q13. Optically denser medium means one with:
a) More mass
b) Higher refractive index
c) Lower refractive index
d) More density
Answer: Higher refractive index.
Why correct: Optical density depends on refractive index, not mass.
Why others wrong:
a & d) Mass density ≠ optical density.
c) Lower index means optically rarer.
Q14. When light enters a denser medium, it:
a) Speeds up
b) Slows down
c) Disappears
d) Changes colour
Answer: Slows down.
Why correct: Greater optical density reduces the speed of light.
Why others wrong:
a) Opposite of refraction rule.
c) Light does not vanish.
d) Colour (frequency) stays unchanged.
Q15. Light bends towards the normal when it travels from:
a) Water to air
b) Air to glass
c) Glass to air
d) Air to vacuum
Answer: Air to glass.
Why correct: Entering a denser medium → speed decreases → bends toward normal.
Why others wrong:
a & c) From denser to rarer, light bends away.
d) No bending between air and vacuum.
Q16. Optically rarer medium means:
a) Lower refractive index
b) Higher refractive index
c) More mass
d) Less transparency
Answer: Lower refractive index.
Why correct: Lower refractive index = less optical density.
Why others wrong:
b) Opposite meaning.
c) Mass density irrelevant.
d) Transparency is unrelated.
Q17. Which medium has refractive index 2.42?
a) Sapphire
b) Diamond
c) Benzene
d) Ruby
Answer: Diamond.
Why correct: Diamond is known for exceptionally high refractive index (2.42).
Why others wrong:
a) ~1.77
c) ~1.50
d) ~1.71
Q18. Light travels faster in:
a) Glass
b) Water
c) Turpentine oil
d) Air
Answer: Air.
Why correct: Light speed decreases as optical density increases; air is least dense optically.
Why others wrong: All others are optically denser and slow down light.
Q19. Which has a refractive index of 1.44?
a) Kerosene
b) Water
c) Ice
d) Turpentine oil
Answer: Kerosene.
Why correct: Table gives kerosene = 1.44.
Why others wrong:
b) 1.33
c) 1.31
d) 1.47
Q20. The refractive index of alcohol is:
a) 1.33
b) 1.36
c) 1.31
d) 1.52
Answer: 1.36.
Why correct: Table lists alcohol = 1.36.
Why others wrong:
a) Water
c) Ice
d) Crown glass
Q21. The ability of a medium to refract light is expressed as its:
a) Mass density
b) Optical density
c) Temperature
d) Thickness
Answer: Optical density.
Why correct: Optical density refers to how strongly a medium bends light.
Why others wrong:
a) Mass density is unrelated.
c) Temperature does not define refracting property.
d) Thickness doesn’t determine refractive power.
Q22. Optical density relates to:
a) Refractive index
b) Mass density
c) Temperature
d) Thickness of medium
Answer: Refractive index.
Why correct: Higher refractive index → higher optical density.
Why others wrong:
b–d) These factors don’t define optical bending ability.
Q23. Which is optically denser?
a) Water (1.33)
b) Kerosene (1.44)
Answer: Kerosene (1.44).
Why correct: Higher refractive index indicates greater optical density.
Why others wrong: Water has lower refractive index → optically rarer.
Q24. A medium with lower refractive index is:
a) Denser
b) Rarer
c) Opaque
d) Translucent
Answer: Rarer.
Why correct: Lower refractive index → optically rarer medium.
Why others wrong:
a) Opposite meaning.
c & d) Transparency is unrelated.
Q25. When light moves from denser to rarer medium, it:
a) Slows down
b) Speeds up
c) Stops
d) Changes frequency
Answer: Speeds up.
Why correct: Speed increases as optical density decreases.
Why others wrong:
a) Opposite.
c) Light never stops.
d) Frequency is constant.
Q26. Bending of light at a boundary is called:
a) Reflection
b) Refraction
c) Scattering
d) Diffraction
Answer: Refraction.
Why correct: Refraction is the change of direction due to change in speed.
Why others wrong:
a) Reflection is bouncing off surfaces.
c) Scattering spreads light.
d) Diffraction bends around obstacles.
Q27. Which medium has refractive index 1.31?
a) Water
b) Ice
c) Kerosene
d) Alcohol
Answer: Ice.
Why correct: Ice is listed as 1.31.
Why others wrong: Others have higher values.
Q28. Benzene has a refractive index of:
a) 1.36
b) 1.44
c) 1.50
d) 1.50
Answer: 1.50.
Why correct: Table lists benzene = 1.50.
Why others wrong:
a) Alcohol
b) Kerosene
Q29. Light bends away from the normal when moving from:
a) Air to water
b) Water to glass
c) Glass to air
d) Air to glass
Answer: Glass to air.
Why correct: Denser → rarer = bends away.
Why others wrong:
a & d) Rarer → denser = bends toward.
b) Both are denser but glass > water.
Q30. Optically denser medium always has:
a) More mass
b) Less transparency
c) Higher refractive index
d) Higher density
Answer: Higher refractive index.
Why correct: Optical density strictly depends on refractive index.
Why others wrong:
a & d) Physical density differs from optical density.
b) Transparency irrelevant.
Q31. The speed of light reduces considerably in:
a) Vacuum
b) Air
c) Glass
d) Space
Answer: Glass.
Why correct: Glass is much denser optically, slowing light the most.
Why others wrong:
a & d) Vacuum/space = maximum speed.
b) Air slows very little.
Q32. The refractive index of sapphire is around:
a) 1.33
b) 1.50
c) 1.71
d) 2.42
Answer: 1.71.
Why correct: Table shows sapphire = 1.71.
Why others wrong:
a) Water
b) Ruby
d) Diamond
Q33. A ray of light changes direction at the boundary because of:
a) Change in frequency
b) Change in speed
c) Change in colour
d) Change in temperature
Answer: Change in speed.
Why correct: Speed change causes bending (refraction).
Why others wrong:
a & c) Frequency and colour remain constant.
d) Temperature doesn’t cause bending directly.
Q34. Rock salt has refractive index about:
a) 1.33
b) 1.44
c) 1.54
d) 1.71
Answer: 1.54.
Why correct: Table lists rock salt = 1.54.
Why others wrong: Others correspond to different materials.
Q35. Which is an optically rarer medium?
a) Diamond
b) Water
c) Air
d) Glass
Answer: Air.
Why correct: Air has refractive index ~1, lowest of all listed.
Why others wrong:
a, b, d) All have higher refractive indices.
Q36. If refractive index increases, speed of light in medium:
a) Increases
b) Decreases
c) Remains same
d) Becomes zero
Answer: Decreases.
Why correct: Light moves slower in optically denser mediums.
Why others wrong:
a) Opposite.
c) Speed changes with medium.
d) Never becomes zero.
Q37. The refractive index of carbon disulphide is:
a) 1.50
b) 1.52
c) 1.63
d) 1.77
Answer: 1.63.
Why correct: Table lists it clearly.
Why others wrong: They belong to other materials.
Q38. Fused quartz has refractive index:
a) 1.46
b) 1.77
c) 1.31
d) 1.63
Answer: 1.46.
Why correct: Given directly in the table.
Why others wrong:
b) Sapphire
c) Ice
d) Carbon disulphide
Q39. Turpentine oil has refractive index:
a) 1.31
b) 1.44
c) 1.47
d) 1.77
Answer: 1.47.
Why correct: Listed as 1.47 in table.
Why others wrong:
a) Ice
b) Kerosene
d) Sapphire
Q40. Ruby has refractive index near:
a) 1.50
b) 1.54
c) 1.65
d) 1.71
Answer: 1.71.
Why correct: Ruby ≈ 1.71.
Why others wrong:
a–c) Do not match table value.
Q41. Light bends more in a medium that is:
a) Less optically dense
b) More optically dense
c) Opaque
d) Rarer
Answer: More optically dense.
Why correct: Higher optical density causes stronger refraction.
Why others wrong:
a & d) Opposite.
c) Opaqueness is unrelated.
Q42. The refractive index of air is approximately:
a) 1.0003
b) 1.1
c) 1.33
d) 2.42
Answer: 1.0003.
Why correct: Air is very close to vacuum, refractive index nearly 1.
Why others wrong:
b) Too high.
c) Water.
d) Diamond.
Q43. When light enters a rarer medium from a denser medium, it bends:
a) Towards normal
b) Away from normal
c) Parallel to normal
d) Not at all
Answer: Away from normal.
Why correct: Speed increases → ray bends away.
Why others wrong:
a) Opposite effect.
c & d) Incorrect for refraction.
Q44. Optical density is not the same as:
a) Mass density
b) Refractive index
c) Ability to refract
d) Light speed
Answer: Mass density.
Why correct: Optical density defines refractive ability, not physical mass density.
Why others wrong:
b & c) Both related to optical density.
d) Speed changes because of optical density.
Q45. A ray of light slows down the most in:
a) Glass
b) Water
c) Air
d) Vacuum
Answer: Glass.
Why correct: Glass has the highest refractive index among these.
Why others wrong:
b) Slows less than glass.
c & d) Very minor or no slowing.
Q46. A medium with refractive index 1.52 is:
a) Ice
b) Water
c) Crown glass
d) Benzene
Answer: Crown glass.
Why correct: Exact value from table.
Why others wrong:
a–d) Correspond to different values.
Q47. Higher optical density implies:
a) Faster light speed
b) Slower light speed
c) No refraction
d) Lower refractive index
Answer: Slower light speed.
Why correct: Speed decreases as optical density increases.
Why others wrong:
a) Opposite.
c) Refraction does occur.
d) Higher—not lower—refractive index.
Q48. In refraction, which remains constant?
a) Speed
b) Wavelength
c) Frequency
d) Velocity
Answer: Frequency.
Why correct: Frequency does not change when light enters another medium.
Why others wrong:
a & d) Speed/velocity change.
b) Wavelength also changes.
Q49. Dense flint glass has refractive index around:
a) 1.44
b) 1.65
c) 2.42
d) 1.33
Answer: 1.65.
Why correct: Table shows dense flint glass = 1.65.
Why others wrong:
a) Kerosene
c) Diamond
d) Water
Q50. Which is an example of optically denser medium than water?
a) Alcohol
b) Ice
c) Kerosene
d) Air
Answer: Kerosene.
Why correct: Kerosene has refractive index 1.44, higher than water’s 1.33.
Why others wrong:
a) 1.36 (slightly higher but kerosene is the best example)
b) 1.31 (lower than water)
d) 1.0003 (much lower)