Please andwer question no. 11,12,13 only in short answer type question

11. Why we are unable to see our surroundings clearly when we enter into a dark cinema hall from outside's bright sunlight. Why our vision improves after some time? Explain.
12. A person can read the number of a distant bus clearly, but he finds difficulty in reading a newspaper.
(i) What is his problem?
(ii) What type of spectacle lens should he use to correct the problem?
13. The power of accommodation of the eye usually decreases with ageing. Suppose when you will be old, which type of eye defect are you likely to suffer, will it be curable. If yes, what types of spectacles you would use?

Dear student, 11)When we are in bright sunlight, the iris of our eyes adjust the pupil in such a way that less light enter our eyes (i.e. the pupil shrinks). But, when we enter a dark room, the iris needs to adjust the pupil in such a way that more light enter our eyes (i.e. the pupil needs to be enlarged). This is because we cannot see anything in a dark room if less light enter our eyes. The adjustment of pupil takes time. So, when we enter from bright sunlight to a dark room, we cannot see initially. 13)Power of accommodation decrease with age because of the following reason: 1.In old age, ciliary muscles becoming weak and the eye lens becoming inflexible or rigid,the eye looses its power of accommodation. 2. Young's modulus of capsular elasticity decreases. 3.Radius of curvature of anterior capsule decreases which makes lens round. It can be corrected by using bifocal lenses. A common type of bi-focal lenses consists of both concave and convex lenses. The upper portion consists of a concave lens. It facilitates distant vision. The lower part is a convex lens. It facilitates near vision. For more post questions in the separate thread so that we can assist you with your doubts. Regards

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