Question

an old age person can read the newspaper by keeping it at 80 cm in front of his eye .what is the nature and power of the lens required to control the problem​

Answer 1

Answer:

The person is suffering from myopia and hence need a concave lens to correct the defect. The lens should be such that an object at infinity must form its image at the far point.

Hence, f=−80 cm=−0.8 m

The power of the lens can be obtained as:

P=

f

1

P=

(−0.8)

1

=−1.25 D

Hope it helps you!!!!!!

Answer 2

Explanation:

The person is suffering from hypermetropia, as near vision = 25cm and he is able to read the newspaper keeping it at 80cm from his eye.

u = -25cm

v = -80cm

1/f =1/v-1/u

1/f =1/-80 + 1/25

1/f =11/400

f =400/11 = 36.3 cm

P = 100/f (Took 100/f as the focal length is in cm)

P = 100/36.3

.°. P = 2.75 D

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