﻿ A lamp and a screen are set up 100 cm apart and a convex lens is placed between them. The two positions of the lens forming real images on the screen are 40 cm apart. What is the focal length of the lens?  : Kaysons Education

# A Lamp And A Screen Are Set Up 100 Cm Apart And A Convex Lens Is Placed Between Them. The Two Positions Of The Lens Forming Real Images On The Screen Are 40 Cm Apart. What Is The Focal Length Of The Lens?

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## Question

### Solution

Correct option is

21 cm

Where now

Therefore x + 40 + x = 100 or x = 30 cm

For lens at L1, we have

u = –30 cm and v = +70 cm. Thus

or                f = +21 cm.

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