Refraction of Light – MCQs with Answers & Explanation
Q1. Which three lie in the same plane according to the first law of refraction?
a) Incident ray, reflected ray and mirrorb) Incident ray, refracted ray and normal
c) Reflected ray, image and mirror
d) Normal, lens and focus
Answer: Incident ray, refracted ray and normal.
Why correct: The first law states these three lie in a single plane.
Why others wrong: Other options include elements not in the law.
Q2. A convex mirror always forms an image that is
a) Real and invertedb) Virtual and erect
c) Real and erect
d) Virtual and inverted
Answer: Virtual and erect.
Why correct: Convex mirrors always form virtual upright images.
Why others wrong: Real images are formed by concave mirrors; virtual images are not inverted.
Q3. The law relating sine of angles of incidence and refraction is called
a) Newton’s lawb) Fresnel law
c) Snell’s law
d) Einstein’s law
Answer: Snell’s law.
Why correct: It gives relation between angles of refraction.
Why others wrong: Other laws are not related to refraction.
Q4. Refractive index of a medium is defined as
a) Angle of bendingb) Ratio of speeds in vacuum to medium
c) Density of medium
d) Color change
Answer: Ratio of speeds in vacuum to medium.
Why correct: n = speed in vacuum / speed in medium.
Why others wrong: Others are effects not definitions.
Q5. The refractive index of medium 2 with respect to medium 1 is written as
a) n12b) n21
c) nm
d) n
Answer: n21.
Why correct: n21 means second medium relative to first.
Why others wrong: Notations are incorrect.
Q6. Refractive index mainly indicates change in
a) Direction onlyb) Speed only
c) Brightness
d) Wavelength
Answer: Speed only.
Why correct: It is a measure of speed reduction.
Why others wrong: They depend on speed change.
Q7. Speed of light is maximum in
a) Waterb) Glass
c) Air
d) Vacuum
Answer: Vacuum.
Why correct: There is no resistance in vacuum.
Why others wrong: Other media reduce speed.
Q8. The value of speed of light in vacuum is
a) 3×10⁶ m/sb) 3×10⁷ m/s
c) 3×10⁸ m/s
d) 3×10⁹ m/s
Answer: 3×10⁸ m/s.
Why correct: Scientifically accepted value.
Why others wrong: Powers are incorrect.
Q9. Speed of light in air is
a) Zerob) Same as vacuum
c) Slightly less than vacuum
d) Much greater
Answer: Slightly less than vacuum.
Why correct: Air has small refractive index.
Why others wrong: Light never becomes zero or faster.
Q10. Speed of light in water compared to air is
a) Greaterb) Same
c) Less
d) Infinite
Answer: Less.
Why correct: Water is optically denser.
Why others wrong: Others violate physics.
Q11. Refractive index from medium 1 to 2 is given by
a) v2/v1b) v1/v2
c) v1+v2
d) v2−v1
Answer: v1/v2.
Why correct: n = speed in first / speed in second.
Why others wrong: Formulae incorrect.
Q12. Refractive index depends mainly on
a) Shape of mediumb) Speed of light in medium
c) Thickness
d) Brightness
Answer: Speed of light in medium.
Why correct: Refractive index is calculated from speed.
Why others wrong: Physical size or brightness do not affect refractive index.
Q13. Angle of incidence is symbolized by
a) rb) i
c) n
d) c
Answer: i.
Why correct: ‘i’ is standard notation.
Why others wrong: They represent other quantities.
Q14. Angle of refraction is symbolized by
a) rb) i
c) n
d) c
Answer: r.
Why correct: ‘r’ denotes refraction angle.
Why others wrong: Other symbols are for incidence or refractive index.
Q15. Refractive index of water is approximately
a) 1.00b) 1.25
c) 1.33
d) 1.54
Answer: 1.33.
Why correct: Accepted scientific value.
Why others wrong: Values incorrect.
Q16. Higher refractive index means
a) Higher speedb) Lower speed
c) Same speed
d) Zero speed
Answer: Lower speed.
Why correct: Refractive index is inversely proportional to speed.
Why others wrong: Light slows in denser media.
Q17. When light enters denser medium, it bends
a) Away from normalb) Towards normal
c) Straight
d) Stops
Answer: Towards normal.
Why correct: Speed reduces in denser medium.
Why others wrong: Refraction direction is well-defined.
Q18. Absolute refractive index is taken with respect to
a) Waterb) Glass
c) Vacuum
d) Air only
Answer: Vacuum.
Why correct: It is measured from vacuum.
Why others wrong: Others give relative index.
Q19. Unit of refractive index is
a) m/sb) m
c) No unit
d) kg
Answer: No unit.
Why correct: It is a ratio.
Why others wrong: Ratios have no unit.
Q20. Normal is drawn
a) Parallel to surfaceb) Perpendicular to surface
c) Slanted
d) Circular
Answer: Perpendicular to surface.
Why correct: Normal is 90° to surface.
Why others wrong: Not true by definition.
Q21. Refraction occurs at
a) Light sourceb) Boundary of two media
c) Mirror
d) Center of lens
Answer: Boundary of two media.
Why correct: Change of medium causes refraction.
Why others wrong: Not zone of change.
Q22. Snell’s law is valid for
a) All colours equallyb) Given colour only
c) Only glass
d) Vacuum only
Answer: Given colour only.
Why correct: Different colours bend differently.
Why others wrong: Dispersion affects validity.
Q23. Refractive index is a
a) Vector quantityb) Scalar quantity
c) Force
d) Energy
Answer: Scalar quantity.
Why correct: No direction involved.
Why others wrong: It just has magnitude.
Q24. No refraction when incidence is
a) Obliqueb) Total
c) Normal
d) Acute
Answer: Normal.
Why correct: No deviation at 90°.
Why others wrong: Refraction occurs otherwise.
Q25. Ratio sin i / sin r is
a) Constantb) Changing
c) Zero
d) Infinite
Answer: Constant.
Why correct: Law of refraction states this.
Why others wrong: It does not randomly change.
Q26. Highest refractive index among the following is
a) Airb) Water
c) Glass
d) Diamond
Answer: Diamond.
Why correct: Diamond is densest optically.
Why others wrong: Others are optically lighter.
Q27. Light slows down in denser medium due to
a) Gravityb) Optical density
c) Magnetism
d) Heat
Answer: Optical density.
Why correct: More resistance to light.
Why others wrong: Not related.
Q28. Refractive index increases when speed
a) Increasesb) Decreases
c) Remains same
d) Becomes zero
Answer: Decreases.
Why correct: Speed and index are inversely related.
Why others wrong: Physics contradiction.
Q29. Glass is optically denser than
a) Diamondb) Water
c) Air
d) Plastic
Answer: Air.
Why correct: Air has lowest refractive index.
Why others wrong: Diamond is denser than glass.
Q30. Refraction proves light changes
a) Shapeb) Speed
c) Mass
d) Color
Answer: Speed.
Why correct: Speed difference causes bending.
Why others wrong: Not proven by refraction.
Q31. Medium with lowest refractive index is
a) Diamondb) Glass
c) Water
d) Air
Answer: Air.
Why correct: Least optical density.
Why others wrong: Denser substances.
Q32. Light bends most in
a) Airb) Glass
c) Water
d) Vacuum
Answer: Glass.
Why correct: Higher refractive index = more bending.
Why others wrong: Lower indices bend less.
Q33. Refractive index of vacuum is
a) 0b) 1
c) ∞
d) 1.33
Answer: 1.
Why correct: n = c/c = 1.
Why others wrong: Incorrect values.
Q34. Refraction occurs in
a) Metals onlyb) Transparent media
c) Vacuum only
d) Mirrors only
Answer: Transparent media.
Why correct: Light passes and bends.
Why others wrong: No bending in opaque.
Q35. Snell’s law relates
a) Angles onlyb) Speeds only
c) Sines of angles
d) Lengths
Answer: Sines of angles.
Why correct: sin i / sin r = constant.
Why others wrong: It does not use lengths or just speeds.
Q36. Refraction causes change in
a) Speed and directionb) Color only
c) Direction only
d) Speed only
Answer: Speed and direction.
Why correct: Both change while entering medium.
Why others wrong: Not complete.
Q37. Formula for refractive index is
a) v/cb) c/v
c) v×c
d) c+v
Answer: c/v.
Why correct: Speed in vacuum / speed in medium.
Why others wrong: Wrong expressions.
Q38. Symbol for refractive index is
a) mb) v
c) n
d) r
Answer: n.
Why correct: International symbol.
Why others wrong: Not used.
Q39. Dispersion is splitting of light due to
a) Reflectionb) Absorption
c) Refraction of different colors
d) Brightness
Answer: Refraction of different colors.
Why correct: Different wavelengths bend differently.
Why others wrong: Not causes dispersion.
Q40. Refractive index varies with
a) Color of lightb) Shape of glass
c) Size of medium
d) Weight
Answer: Color of light.
Why correct: Wavelength dependent.
Why others wrong: Irrelevant factors.
Q41. When light enters rarer medium, it bends
a) Towards normalb) Away from normal
c) Backwards
d) Stops
Answer: Away from normal.
Why correct: Speed increases in rarer medium.
Why others wrong: Wrong physical behavior.
Q42. Refractive index compares speed of light in
a) Same mediumb) Two media
c) Mirror and lens
d) Air only
Answer: Two media.
Why correct: It’s a ratio.
Why others wrong: Refractive index requires reference medium.
Q43. Smaller wavelength bends
a) Lessb) Same
c) More
d) Not at all
Answer: More.
Why correct: High frequency refracts more.
Why others wrong: Not supported by physics.
Q44. Optical density relates to
a) Massb) Speed of light
c) Volume
d) Color
Answer: Speed of light.
Why correct: Lower speed means denser medium.
Why others wrong: No relation.
Q45. Light does not refract when traveling in
a) Glass onlyb) Liquid only
c) Same medium
d) Air only
Answer: Same medium.
Why correct: No speed change.
Why others wrong: Refraction occurs at boundary.
Q46. Denser medium has
a) Higher refractive indexb) Lower refractive index
c) Same index
d) Infinite index
Answer: Higher refractive index.
Why correct: Light slows down.
Why others wrong: Physically incorrect.
Q47. Visible bending is seen when light strikes surface
a) Normalb) Obliquely
c) Parallel
d) From behind
Answer: Obliquely.
Why correct: Bending occurs only when angle exists.
Why others wrong: No change at normal.
Q48. Change in speed causes change in
a) Directionb) Color
c) Brightness
d) Energy
Answer: Direction.
Why correct: Bending follows speed change.
Why others wrong: Not directly affected.
Q49. Glass slab causes refraction because it has
a) Higher temperatureb) Different optical density
c) Rough surface
d) Color
Answer: Different optical density.
Why correct: Speed changes.
Why others wrong: Irrelevant causes.
Q50. Medium with highest refractive index among given is
a) Airb) Water
c) Glass
d) Diamond
Answer: Diamond.
Why correct: Highest optical density.
Why others wrong: Lower refractive indices.