(3)

At noon, the sun is directly overhead and has lesser air to travel through, thus the distance to be travelled in air is reduced. Less scattering leads to the sun appearing white as only a little of the blue and violet colour is scattered.

(4)

Twinkling of stars is due to atmospheric refraction of starlight. The refraction of light occurs in a medium of various layers of gradually changing refractive indices. A star always emits light but the different layers of refractive indices in our atmosphere allow it to seem like a twinkle. When light enters the earth and hits the atmosphere from a distance, it begins to refract the light into any layer it reaches. Thus, the star appears to twinkle.

(4)

When white light enters a glass prism from air, the angle of deviation is least for red light. The white light consists of seven colours in which violet has the least wavelength and red colour has the maximum wavelength.

(4)

The white light consists of seven colours. Violet has the least wavelength, so its deviation is maximum. Red has the maximum wavelength, so its deviation is minimum.

(4)

Cataract is the medical condition in which the lens of the eyes becomes progressively opaque, resulting in blurred vision.