The Human Eye and the Colourful World – Very Short Answer Type Questions
60 Very Short Answer Questions — The Human Eye and the Colourful World
CBSE Board Examination Focus:
- Short, precise answers for quick recall.
- Concept clarity: definitions, causes and corrections.
- Labelled diagrams and formula recall (lens formula, power).
Instructions: These 60 Very Short Answer Questions with answers follow the NCERT textbook content. Use them for quick revision and last-minute practice.
Very Short Answer Questions (1–60)
1. What is the cornea?Answer: The transparent front surface of the eye that does most of the refraction of light entering the eye.
2. What is the pupil?Answer: The aperture in the centre of the iris through which light enters the eye.
3. Define iris.Answer: The coloured muscular diaphragm that controls the size of the pupil and amount of light entering the eye.
4. What is the function of the lens in the eye?Answer: To fine-tune focus by changing shape (accommodation) so that images form on the retina.
5. Where is the retina located?Answer: The retina is the light-sensitive inner lining at the back of the eye where the image is formed.
6. What does the optic nerve do?Answer: It transmits visual signals from the retina to the brain.
7. What do photoreceptor cells do?Answer: Rods and cones detect light and colour and convert them into nerve impulses.
8. What is accommodation?Answer: The process by which the eye changes the focal length of the lens to focus on near or distant objects.
9. How does the lens change for near vision?Answer: The ciliary muscles contract, making the lens thicker and more convex.
10. How does the lens change for distant vision?Answer: The ciliary muscles relax, making the lens thinner and less convex.
11. What type of image is formed on the retina?Answer: A real and inverted image is formed on the retina.
12. Why does the brain perceive the image as upright?Answer: The brain processes and interprets the inverted retinal image so we perceive it as upright.
13. Define myopia.Answer: Short-sightedness; difficulty seeing distant objects clearly because image forms in front of the retina.
14. Which lens corrects myopia?Answer: A concave (diverging) lens is used to correct myopia.
15. Define hypermetropia.Answer: Long-sightedness; difficulty seeing close objects because image forms behind the retina.
16. Which lens corrects hypermetropia?Answer: A convex (converging) lens is used to correct hypermetropia.
17. What is presbyopia?Answer: Age-related loss of accommodation due to stiffening of the lens, causing difficulty focusing on near objects.
18. What is a cataract?Answer: Clouding of the eye lens that reduces vision; usually treated surgically by replacing the lens.
19. State the lens formula.Answer: 1/f = 1/v - 1/u, where f = focal length, u = object distance, v = image distance.
20. How is power of a lens defined?Answer: Power P = 1/f (in metres), measured in dioptres (D).
21. What is the sign of focal length for a convex lens?Answer: Positive (+) for a convex (converging) lens.
22. What is the sign of focal length for a concave lens?Answer: Negative (−) for a concave (diverging) lens.
23. What is dispersion of light?Answer: Splitting of white light into its constituent colours due to wavelength-dependent refraction.
24. Which colour bends most in a prism?Answer: Violet light bends the most.
25. Which colour bends least in a prism?Answer: Red light bends the least.
26. What is the order of colours in visible spectrum?Answer: Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV).
27. What causes the blue colour of the sky?Answer: Rayleigh scattering of shorter (blue) wavelengths by air molecules.
28. Why are sunsets red?Answer: During sunrise/sunset, sunlight passes a longer path; blue light is scattered out leaving red hues.
29. What is Rayleigh scattering?Answer: Scattering of light by particles much smaller than the wavelength, wavelength-dependent (∝1/λ^4).
30. What is the Tyndall effect?Answer: Scattering of light by colloidal-sized particles, visible as light beams in dusty air.
31. How is a rainbow formed?Answer: By dispersion, refraction and internal reflection of sunlight in water droplets, producing a spectrum of colours.
32. Which rainbow is brighter, primary or secondary?Answer: The primary rainbow is brighter than the secondary one.
33. Why does a secondary rainbow have reversed colours?Answer: It involves two internal reflections, reversing the order of colours.
34. State one use of prisms in experiments.Answer: Prisms are used to disperse white light into its component colours for study.
35. What determines the colour of an object?Answer: The wavelengths of light it reflects; other wavelengths are absorbed.
36. Why does a red cloth appear black under green light?Answer: Because red cloth reflects red wavelengths but absorbs green, so under green light it appears dark/black.
37. What is lateral inversion? (In context of mirrors)
Answer: Lateral inversion is the left-right reversal seen in images in a plane mirror.
38. Does dispersion occur in reflection?Answer: No, dispersion occurs due to refraction where refractive index varies with wavelength.
39. Name two defects of vision corrected by lenses.Answer: Myopia and hypermetropia (also presbyopia).
40. What is the near point of a normal human eye?Answer: Approximately 25 cm for a young adult with normal accommodation.
41. What is the far point of a normal eye?Answer: Infinity (the eye can see distant objects clearly without accommodation).
42. What is the role of ciliary muscles?Answer: To change the curvature of the lens for accommodation.
43. What type of lens is used in reading glasses for presbyopia?Answer: Convex lens or bifocals are used to aid near vision.
44. What happens to focal length when the lens becomes more convex?Answer: The focal length decreases (becomes shorter), increasing converging power.
45. Define magnification for lenses.Answer: Magnification m = v/u (ratio of image distance to object distance) or m = height of image/height of object.
46. For a concave lens, is the image virtual or real for a real object?Answer: Virtual, erect and diminished image is formed on the same side as the object.
47. How does adding smoke/dust affect the path of a beam of light in a room?Answer: Particles scatter the light (Tyndall effect), making the beam visible.
48. What is meant by white light?Answer: White light is a mixture of all visible wavelengths/colours of light.
49. Can dispersion occur in a glass slab? Explain briefly.Answer: No significant dispersion like a prism; a slab causes parallel displacement but little angular dispersion.
50. State one real-life example of scattering other than sky colour.Answer: The bluish appearance of distant mountains due to scattering of light by the atmosphere.
51. What is the principal focus of a lens?Answer: The point where parallel rays of light converge (convex) or appear to diverge from (concave) after refraction.
52. What is the focal length of a plane mirror?Answer: A plane mirror has infinite focal length; it does not converge/diverge rays.
53. In what direction does red light deviate compared to violet in a prism?Answer: Red deviates less than violet; red is least deviated, violet most deviated.
54. Why do clouds appear white?Answer: Cloud droplets scatter all wavelengths nearly equally (Mie scattering), so clouds appear white.
55. Give one difference between dispersion and scattering.Answer: Dispersion is wavelength-dependent refraction separating colours; scattering is redirection of light by particles.
56. What is meant by 'visible spectrum'?
Answer: The range of wavelengths of light visible to the human eye (~400–700 nm), seen as colours from violet to red.
57. What role do cones play in vision?Answer: Cones detect colour and function best in bright light conditions.
58. What role do rods play in vision?Answer: Rods detect low light intensity and help in night vision but do not detect colour.
59. Give one precaution while drawing ray diagrams for lenses.Answer: Use a straightedge, label principal axis, focal points, object and image clearly and maintain scale where possible.
60. Why should diagrams be labelled in exams?Answer: Neat, labelled diagrams fetch marks and show clear understanding of concepts.