Vardaan Learning Institute

Ans: (d) Retina
Retina acts as the light-sensitive screen where the image is formed.

Ans: (c) Ciliary muscles
Ciliary muscles relax (lens thin) and contract (lens thick) to adjust focal length.

Ans: (c) Iris
The iris controls the size of the pupil and thus the amount of light entering the eye.

Ans: (c) 25 cm
For a normal young adult eye, the near point is 25 cm.

Ans: (b) Infinity
A normal eye can see objects clearly up to infinity.

Ans: (c) Refraction, dispersion and internal reflection
Three steps: Refraction into drop, Dispersion, Internal Reflection, Refraction out of drop.

Ans: (b) -0.5 D
$f = -Far Point = -2m$.
$P = 1/f = -0.5$ D.

Ans: (b) Cylindrical lens
Astigmatism is due to irregular curvature of cornea, corrected by cylindrical lens.

Ans: (d) Red
Red has the longest wavelength and bends the least; Violet has the shortest.

Ans: (a) Blue color is scattered most
Fine particles scatter short wavelengths (blue/violet) more effectively (Rayleigh scattering).

Ans: (a) Both A and R are true and R is the correct explanation of A.
At high altitudes, atmosphere is thin or non-existent, so no scattering occurs, leading to a dark sky.

Ans: (a) Both A and R are true and R is the correct explanation of A.
Light travels less distance; scattering is minimal, so all colors reach the eye combined as white.

Ans: (a) Both A and R are true and R is the correct explanation of A.
Planets are extended sources (collection of point sources). Variations cancel out, giving a steady light.

Ans: (a) Both A and R are true and R is the correct explanation of A.
Red has longest wavelength $\rightarrow$ least scattered $\rightarrow$ visible from long distances even in fog.

It is the ability of the eye lens to adjust its focal length to see objects clearly at varying distances (from 25 cm to infinity). For a normal eye, the power of accommodation is about 4 Dioptres.

Defect: Myopia (Nearsightedness). Corrective Lens: Concave Lens.
$v = -1.2 m, u = \infty$.
$P = 1/f = 1/(-1.2) = -0.83$ D.

1. Wider field of view (approx $180^\circ$ vs $150^\circ$ with one eye).
2. Stereopsis (3D vision/Depth perception): Ability to judge distances accurately.

Caused by atmospheric refraction. As starlight enters the atmosphere, it undergoes refraction due to changing refractive index of air layers. The apparent position of the star fluctuates, and the intensity of light reaching the eye varies, causing the twinkling effect.

(Diagram required showing Incident ray, Refracted ray, Emergent ray, Angle of Prism A, Angle of Deviation D).

Defect where the eye loses its power of accommodation due to aging. The near point recedes.
Cause: Weakening of ciliary muscles and diminishing flexibility of eye lens.
Correction: Bifocal lens (Upper concave for distance, Lower convex for reading).

(i) Farsightedness (cannot see near objects). Causes: Short eyeball or long focal length of lens.
(ii) Corrected by Convex Lens (Diagram required showing convergence on retina).
(iii) +1.5D is positive $\rightarrow$ Convex Lens $\rightarrow$ Hypermetropia.
$f = 1/1.5 = 0.67$ m = $66.7$ cm.

(i) Use two prisms. First disperses into spectrum. Second (inverted) recombines spectrum into white light.
(ii) Blue Sky: Scattering of lower wavelengths (blue) by air molecules.
(iii) Red Sun: At horizon, light travels longer distance. Blue scattered out. Red reaches eye.

(i) Red.
(ii) Violet.
(iii) VIBGYOR (Violet to Red).

(i) Advanced sunrise: 2 mins. Delayed sunset: 2 mins. Total: 4 mins.
(ii) Light from star bends towards normal as it enters atmosphere, so they appear higher.
(iii) They are extended sources; point-source variations average out.