Question

(a) Explain the functions of the following parts of the eye :
(a) cornea (b) iris (c) pupil (d) ciliary muscles (e) eye-lens
(f) retina (g) optic nerve
(b) If you walk from a dark room into sunlight and back again into dark room, how would your pupils after in size ? What makes this happen ?
(c) Explain why, we cannot see our seats first when we enter a darkened cinema hall from bright light but gradually they become visible.

Answer 1

(a) a. Cornea: It is the front part of the eye. The light coming from objects enters the eye through cornea.
b. Iris: It controls the amount of light entering the eye.
c. Pupil: It controls the illumination in the eye.
d. Ciliary muscles: The focal length of the eye-lens can be changed by changing its shape by the action of ciliary muscles.
e. Eye-lens: It focuses light on to the retina.
f. Retina: It is a delicate membrane having a large number of light sensitive cells called 'rods' and 'cones' which respond to the intensity of light and colour of objects respectively.
g. Optic nerve: It conveyes the image formed on the retina to the brain.

(b) If we walk from a dark room into sunlight, the pupil of the eye contracts. On again entering the dark room, the pupil of the eye expands.

(c) When we enter a darkened cinema hall from bright sunshine, at first we cannot see our seats clearly but gradually they become visible. This is because in bright sunshine the pupil of our eye is small and when we just enter the darkened room very little light enters our eye due to which we cannot see properly. After a while, when the pupil of our eye expands, more light enters our eye and we can see clearly.