Question

a convex lens of focal length 50 cm is placed 20cm in front of a plane mirror. light from very far away source falls on the lens the distance of final image from the mirror is what ??​

Answer 1

Answer:

The correct answer of this question is $40 cm$

Explanation:

Given - A convex lens of focal length 50 cm is placed 20cm in front of a plane mirror.

To Find  -  Write  the distance of final image from the mirror.

According to the question -

Now, the lens formula is,

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

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

$\frac{1}{20} - \frac{1}{12}$

$\frac{1}{4} ( \frac{1}{5} - \frac{1}{3} )$

$= - \frac{1}{4} ( \frac{2}{15} )$

Image distance for the convex lens , $v = - 30 cm$

And the distance of image formed by lens from mirror = $40cm$

Therefore , final image formed behind the mirror = $40cm$

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