(a) The ability of eye lens to adjust its focal length to form the sharp image of the object at varying distances on the retina is called its power of accommodation.
(b)v = 1.2 m= -120 u = \(\infty\)
P of the corrective lens=?
Bye lens formula
\({1\over v}-{1\over u}={1\over f}\)
\(\Rightarrow\ {1\over -120}-{1\over \infty}={1\over f}\)
\(\Rightarrow\ {-1\over 20}-0={1\over f}\left(\therefore{1\over \infty}=0 \right)\)
\(\Rightarrow\ {-1\over 120}={1\over f}\)
\(\therefore\ f=-120cm\)
Thus the corrective lens for the above defect is concave lens (as focal length has - ve sign) of focal length of 120 cm
(c)\(P={1\over f(in\ metres)}={1\times 100\over -120}=-0.83D\)

(i)Refractive index of a medium is different for colour of light
(ii)Due to large wavelength, red colour is least scattered and travel to large distance.

(a) The ability of eye lens to adjust its focal length to form the sharp image of the object at varying distances on the retina is called its power of accommodation.
(b) When we see the nearby object the cillary muscles contract, it increases the thickness of eye lens. The eye lens then becomes thicker. As a result the focal length of eye lens decreases in such a way that the clear sharp image of nearby object is formed on the retina. Thus, the object is seen clearly to us. When we see the distant object these muscles becomes relaxed, thus the eye lens becomes thinner, and consequently focal length of the lens increases. Therefore, the parallel rays coming from the distant object are focused on the retina and object is seen clearly to us Thus the accommodation power of an eye helps a person to see nearby as well as distant objects clearly

Real and inverted.

25cm

Since there is no atmosphere, there would be no scattering of light. Hence the colour of the sky will be dark.

Towards the normal

Different colours travel through prism with different speeds and have different refractive index

During sunrise/sunset, the looks reddish. This is because at this because at this stage, rays from the sun have to travel a much larger part of atmosphere. The red colour having largest wavelength is scattered the least.
At noon, the sun is nearly overhead. The sunlight has to pass through much smaller portion of earth's atmosphere the scattering is much less and the sun looks white.

(i) The structures of the eye such as cornea, pupil, ciliary muscles, eye lens, aqueous humour and vitreous humour etc.,
(ii) The retina of the eye which converts light signals to electrical impulses and 
(iii) Optic nerve that transmit electrical impulses to brain.

Stars twinkle due to atmospheric refraction of starlight. The starlight passes through different layers of atmospheric medium of gradually changing refractive index. So, it is refracted multiple times. As the apparent position of star and the physical condition of the earth's atmosphere are not constant the amount of starlight entering the eye flickers and gives a twinkling effect.

(a) Functions of the following parts of human eye:
(i) Comea: Objects enters the eye through cornea.
(ii) Iris: Iris controls the size of the pupil.
(iii) Crystalline lens: It focuses the image of the object on the retina.
(iv) Ciliary muscles: Ciliary muscles hold the eye lens and change the thickness of eye lens while focussing.
(b) (i) Objective of such campaigns. To make people aware of corneal blindness and make them realise their duties towards the society by taking pledge for eye donation.
(ii) (a) One pair of eyes can give eyesight to two corneal blind persons and make them see this beautiful world.
(b) Our eyes can live even after our death. People belonging to all age groups, even people with medical conditions like cataract, diabetes, hypertension can donate their eyes.
(iii) Values developed in persons who actively participate in such programmes:
(a) Concern for others and social welfare.
(b) Responsible behaviour and awareness.

(a) (i) Myopia: Short-sightedness is caused due to excessive is caused due to excessive curvature in cornea or elongation of eyeball. Image is formed before of the retina. So, a concave lens is used to correct it.
(ii) Astigmatism: The inability to focus the light n both vertical and horizontal lines is called astigmatism. It is caused due to varying curvature in lens both horizontally and vertically. It is corrected by using cylindrical lens.
(iii) Bifocal lenses: These are used to correct presbyopic eye. These contain lenses with upper concave and lower convex surface. Presbyopia arises with age.
(b) The focal length of the lens cannot be changed up to an extent that objects nearer than 25 cm can be viewed. So it is not able to focus for 10 cm.