Question

A person cannot see the objects beyond 600 cm. Find the power of lens he should use to correct this defect.
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Answer 1

Given ,

A person cannot see the objects beyond 600 cm

Thus ,

Object distance (u) = - ∞

Image distance (v) = - 600 cm

We know that , the lens formula is given by

$\boxed{ \sf{ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} }}$

Thus ,

1/f = -1/600 - (-1/∞)

1/f = -1/600 + 1/∞

1/f = -1/600

f = -600 cm or -6 m

Now , the power of lens is given by

$\boxed{ \sf{Power \: of \: lens \: (P) = \frac{1}{f \: (in \: m)}} }$

Thus ,

P = -1/6

P = -0.16 D

The negative sign of P shows the lens is concave

Therefore ,

• The power of lens required to correct the vision is -0.16 D