CBSE Class 10 Science 2018 · Paper 31/1 · Question 20(b)

(a) (i) Cornea: light enters the eye through this transparent front surface, and most of the refraction of the light entering the eye takes place at it. (ii) Iris: controls the size of the pupil, and so the amount of light entering the eye. (iii) Crystalline lens: converges the light rays to form a real, inverted image on the retina, providing the fine adjustment of focal length needed for objects at different distances. (iv) Ciliary muscles: change the curvature, and so the focal length, of the eye lens by relaxing and contracting, so that a sharp image forms on the retina (accommodation). (b) Early in the morning the Sun is near the horizon, so its light has to travel a much larger distance through the atmosphere. Most of the blue light and other shorter wavelengths are scattered away by the particles of air, and mainly the longer wavelengths, such as red, reach our eyes; so the Sun appears reddish. No, an astronaut on the Moon will not observe this, because the Moon has no atmosphere to scatter the sunlight.