1.
[Diagram: Human Eye with Cornea, Iris, Pupil, Crystalline Lens, Ciliary
Muscles, Retina, Optic Nerve labeled]
2. It provides fine adjustment of focal length required to
focus objects at different distances on the retina.
3. Iris controls the size of the pupil. Pupil regulates
the amount of light entering the eye (dilates in dim light, constricts in bright light).
4. The ability of the eye lens to adjust its focal length
is called accommodation. Maximum power = 4 D.
5. It is the junction of the optic nerve and retina. No
photoreceptor cells (rods/cones) are present, so no vision is possible here.
6. Retina acts as a screen to form the image. Cells: Rods
(intensity/dim light) and Cones (color/bright light).
7. In bright light, pupil is small. Upon entering dark, it
takes time to expand (dilate) to allow more light. This time lag causes temporary blindness.
8. Range: 25 cm to Infinity. Near Point = 25 cm. Far Point
= Infinity.
9. Ciliary muscles change the curvature of the eye lens to
change its focal length ($f$), keeping the image distance ($v$) constant (distance between lens and retina).
10. Ciliary muscles modify the curvature of the eye lens
to focus objects at varying distances.
11. Transmits electrical signals generated by retina to
the brain for processing.
12. (i) Wider field of view ($180^\circ$ vs $150^\circ$).
(ii) Depth perception (3D vision).
13. The pupil constricts (becomes smaller) to reduce light
entry.
14. Real and Inverted. Because the eye lens is a convex
lens.
15. Suspensory ligaments connected to the ciliary muscles.
16. Myopia: Near-sightedness. Distant objects are
blurred. Image forms in front of retina.
[Diagram: Myopic Eye - Rays converging before retina]
17. Corrected by Concave Lens.
[Diagram: Correction of Myopia with Concave Lens]
18. (i) Excessive curvature of eye lens. (ii) Elongation
of eyeball.
19. Hypermetropia: Far-sightedness. Near objects
are blurred. Image forms behind retina.
[Diagram: Hypermetropic Eye - Rays meeting behind retina]
20. Corrected by Convex Lens.
[Diagram: Correction of Hypermetropia with Convex Lens]
21. (i) Focal length of eye lens is too long. (ii) Eyeball
is too short.
22. Myopic: Near point is normal (25 cm), Far point is
less than infinity. Hypermetropic: Near point is > 25 cm, Far point is normal.
23. Presbyopia: Old-age hypermetropia due to
weakening of ciliary muscles and hardening of lens.
24. Bifocal lens (Upper: Concave for distance, Lower:
Convex for reading).
25. Defect: Myopia (Near-sightedness). Lens: Concave Lens.
26. Power $P = -5.5$ D. $f = 1/P = -1/5.5 = -0.18$ m = -18
cm. Defect: Myopia.
27. Power $P = +1.5$ D. $f = 1/1.5 = +0.67$ m = +67 cm.
Defect: Hypermetropia/Presbyopia.
28. A hypermetropic eye has a normal Far Point (infinity).
They only need convex lens (+ power) to read/see near objects, not for distance.
29. Yes, Presbyopia often accompanies Myopia. Correction:
Bifocal lenses.
30. Clouding of the crystalline lens in old age, leading
to loss of vision. Correction: Cataract Surgery (IOL implantation).
31.
[Diagram: Refraction through Prism showing i, r, e, D]
32. Angle between incident ray and emergent ray. Depends
on: Angle of prism (A), Refractive index ($n$), Angle of incidence ($i$).
33. Splitting of white light into constituent colors
(VIBGYOR).
34. Least bends: Red (Max wavelength). Most bends: Violet
(Min wavelength). $Deviation \propto 1/\lambda$.
35. Different colors have different speeds in glass
(refractive index varies with wavelength: $n_v > n_r$), so they bend by different angles.
36.
[Diagram: Spectrum formation on screen]
37. Isaac Newton. Recombination: Two identical prisms
placed inverted to each other; first disperses, second recombines to form white light.
38. No. $Speed = c/n$. Since $n$ is different for
different colors, speed is different (Red is fastest, Violet is slowest in glass).
39. Natural spectrum caused by dispersion of sunlight by
raindrops. Steps: Refraction, Dispersion, Total Internal Reflection, Refraction.
40. (i) Sun behind observer. (ii) Water droplets
(rain/mist) in front.
41. Because raindrops are spherical, and the cone of rays
reaching the eye from all such drops forms a circular arc.
42. Monochromatic means single color/wavelength. No, prism
cannot disperse it (only deviation occurs).
43. Because Red has the longest wavelength, its refractive
index is lowest, so it deviates least.
44. Glass slab: Emergent ray parallel to incident (Lateral
shift only, no dispersion recombines). Prism: Emergent ray deviates (Angular dispersion).
45. Primary: One internal reflection (Brighter, Red
outer). Secondary: Two internal reflections (Fainter, Violet outer).
46. Refraction of light by earth's atmosphere due to
varying optical density of air layers (fluctuating temperature/density).
47. Stars are point sources; atmospheric turbulence causes
path of light to fluctuate, changing intensity (twinkle). Planets are extended sources; fluctuations cancel
out.
48. Light from stars bends towards normal as it enters
denser lower atmosphere. Eye traces ray back in straight line, seeing star at a higher apparent position.
49. Sun is visible 2 mins before actual sunrise and 2 mins
after sunset due to atmospheric refraction. Total day length increases by 4 mins.
50. Due to continuous change in density and refractive
index of atmospheric air layers.
51. Phenomenon of spreading of light by minute particles.
Depends on particle size ($a$) vs wavelength ($\lambda$).
52. Scattering of light by colloidal particles. Examples:
Sunlight through canopy, Dust beam in dark room.
53. Rayleigh Scattering: Air molecules are smaller than
wavelength of visible light. They scatter blue light (shorter $\lambda$) more than red (longer $\lambda$).
54. Black. No atmosphere to scatter light.
55. Red has longest wavelength, scattered least by
fog/smoke, so it can travel long distances to reach the eye.
56. At horizon, light travels longer distance through
atmosphere. Blue is scattered away; only Red/Orange (longer $\lambda$) reaches our eyes.
57. At noon, sun is overhead. Light travels shorter
distance. Scattering is less, all colors reach eye $\to$ appear white.
58. Water molecules absorb red wavelengths and scatter
blue wavelengths.
59. $Intensity \propto 1/\lambda^4$. (Shorter wavelength
scatters much more).
60. Smoke particles are larger than air molecules but
small enough to scatter blue end of spectrum preferentially.
