Question

Far point of a person is 5m. In order that he has normal vision what kind of spectacles should be used
A) concave lens with focal length 5 m
B) concave lens with focal length 10 m [ ]
C) convex lens with focal length 5 m
D) convex lens with focal length 2.5 m​

Answer 1

Answer:

a because it is the disorder of myopia and couldn't see farer objects

Explanation:

it is corrected bi.concave lens and its focal length is -D then f=-D

Answer 2

HEY MATE YOUR ANSWER IS HERE

the person have far-sightedness hence

person is suffering from myopia

NOW

U ( object distance ) = ∞

v ( image distance ) = -5m [ as v is negative ]

f = ?

by lens formula .....

$\frac{1}{f} = \frac{1}{ \infty } + \frac{1}{v}$

$\frac{1}{f} = \frac{1}{ \infty } + \frac{1}{ - 5}$

$\frac{1}{f} = \frac{1}{ - 5}$

$f = - 5 \: metre$

HENCE OPTION A IS CORRECT

CONCAVE LENS WITH FOCAL LENGTH -5 m