Question

The power of lens is -5D. Define its
Principal focus and calculate its focal
length.​

Answer 1

Given:-

P = -5 D

To find :-

It's focal length.

Answer :-

F = -20 cm

Principal focus :- The principal focus is a point present in the principal axis of a lens or mirror such that when a ray coming parallel to the principal axis must passes through it.

We have,

P = -5 D

that means it's is a convex lens and it's focal length is also in negative.

using power formula,

$\boxed{\sf{ P = \dfrac {100}{f}}}$

Now put the value,

$\implies$ $-5 = \dfrac {100}{f}$

$\implies$ $f = \dfrac {-100}{5}$

$\implies$ $f = -20 cm$

hence,focal length is -20 cm.

Answer 2

Answer:

His

Explanation:

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