⭐ 50 Light & Optics – High-Level GK Questions with Explanations

Light & Optics is one of the most important chapters for competitive exams. Many tricky questions are asked from reflection, refraction, total internal reflection, mirrors, lenses, prisms, and optical instruments.
Below are 50 exam-focused Light and Optics questions with clear answers and explanations.

📘 Top 50 Light & Optics GK Questions with Answers

1. What is the speed of light in a vacuum?

Answer: 3 × 10⁸ m/s
Explanation: Light travels fastest in a vacuum and slower in air, water, or glass.

2. What type of wave is light?

Answer: Electromagnetic transverse wave
Explanation: It does not require a medium to propagate.

3. Which scientist proved the speed of light is finite?

Answer: Ole Rømer
Explanation: He studied Jupiter’s moon Io.

4. Which scientist discovered that light has wave nature?

Answer: Thomas Young
Explanation: Young’s Double Slit Experiment (YDSE).

5. Who established light’s particle nature?

Answer: Albert Einstein
Explanation: Photoelectric effect.

6. What is reflection of light?

Answer: Bouncing back of light from a surface.

7. What is refraction of light?

Answer: Bending of light while passing from one medium to another.

8. Which law explains reflection?

Answer: Laws of reflection

Angle of incidence = angle of reflection
Incident ray, reflected ray, normal lie on same plane

9. What is Snell’s Law used for?

Answer: Refraction
Formula: n₁ sin i = n₂ sin r

10. What is refractive index?

Answer: Ratio of speed of light in vacuum to speed in medium.
Formula: n = c/v

11. Which colour has maximum refraction?

Answer: Violet
Explanation: Has shortest wavelength.

12. Which colour has minimum refraction?

Answer: Red
Explanation: Longest wavelength.

13. What is dispersion of light?

Answer: Splitting of white light into seven colours.

14. What instrument demonstrates dispersion?

Answer: Prism
Explanation: Separates colours based on wavelength.

15. What is total internal reflection (TIR)?

Answer: When light reflects fully inside a denser medium.

16. What is the critical angle?

Answer: Angle of incidence beyond which TIR occurs.

17. Which device uses TIR?

Answer: Optical fibre
Explanation: Used in internet transmission.

18. Why does a diamond shine brightly?

Answer: Due to high refractive index → intense TIR.

19. What type of mirror is used in car side mirrors?

Answer: Convex mirror
Explanation: Gives wider field of view.

20. What type of mirror is used by dentists?

Answer: Concave mirror
Explanation: Forms enlarged upright image.

21. What mirror is used in solar cookers?

Answer: Concave mirror
Explanation: Concentrates sun rays.

22. What is focal length?

Answer: Distance between mirror/lens and focus point.

23. What is power of a lens?

Answer: P = 1/f (in meters)
Unit: Dioptre (D)

24. Which lens has positive power?

Answer: Convex lens
Explanation: Converging lens.

25. Which lens has negative power?

Answer: Concave lens
Explanation: Diverging lens.

26. Which lens is used to correct myopia?

Answer: Concave lens
Explanation: Spreads out light.

27. Which lens is used to correct hypermetropia?

Answer: Convex lens
Explanation: Converges light.

28. What is chromatic aberration?

Answer: Failure of lens to form a single image for all colours.

29. What is spherical aberration?

Answer: Rays at different distances from principal axis focus at different points.

30. What is diffraction of light?

Answer: Bending of light around obstacles.

31. What is interference of light?

Answer: Superposition of two coherent light waves.

32. What experiment confirmed interference?

Answer: Young’s Double Slit Experiment.

33. What is polarization?

Answer: Restriction of light vibration in one plane.

34. Which light can be polarized?

Answer: Transverse waves only.

35. Why is the sky blue?

Answer: Rayleigh scattering of shorter wavelengths (blue).

36. Why is the sunset red?

Answer: Longer wavelengths (red) scatter less, reach the eye more.

37. What is optical density?

Answer: Ability of a medium to slow down light.

38. What is optical path length?

Answer: Physical distance × refractive index.

39. What creates a rainbow?

Answer: Dispersion + Reflection + Refraction in water droplets.

40. Which instrument uses lenses for magnification?

Answer: Microscope / Telescope

41. What is focal plane?

Answer: Plane where refracted or reflected rays meet.

42. What is the principal axis?

Answer: Imaginary line passing through centre of curvature and pole.

43. What is a collimated beam?

Answer: Light rays that are parallel (e.g., laser).

44. Which light source is monochromatic?

Answer: Laser
Explanation: Single wavelength.

45. What is Brewster’s angle?

Answer: Angle of incidence at which reflected light becomes completely polarized.

46. What is the unit of luminous intensity?

Answer: Candela

47. What is the unit of illumination?

Answer: Lux

48. What is fluorescence?

Answer: Emission of light immediately when excited.

49. What is phosphorescence?

Answer: Delayed emission of light (glow-in-the-dark).

50. What is a hologram?

Answer: 3D image created using laser interference.

⭐ Conclusion

These 50 Light and Optics GK Questions with Explanations are essential for competitive exams. Understanding these concepts improves accuracy in Physics MCQs for SSC, Railway, NTPC, UPSC, CDS, NDA, Banking & more.