Question

OR
24) Suresh gets his eye checked and doctor prescribes +4.0 D. What type of len should he wear ? also find its focal length
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Answer 1

Answer:

He should wear convex lens and the focal lenth of the lense is 25cm.

Answer 2

focal length of lens is +0.25m

Given:

power = +4.0 D

solution:

• if the power of a lens is positive, the focal length is positive, and lens used are convergent(convex lens)

• if the power of a lens is negative, the focal length is negative, and lens used are convergent(concave lenses)

• according to the given question, as the power is positive (+4D) Suresh need to wear convex lens

now,

power = 1/f

4D = 1/f

f = 1/4

f = +0.25m

focal length of lens is +0.25m

hence, focal length is +0.25m and convex lens should be used