Question

how to find object distance if only focal length is given?

Answer 1

Answer:

use the below formula

Explanation:

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

where f is Focal length, u is object distance and v is image distance

if the image is said to be sharp, v = f

so,

$f = \frac{uv}{u + v}$

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