Question

at what distance should an object be placed in front of converging lens of focal length 20cm so that its 5 times magnified image is formed on screen. draw ray diagram

Answer 1

Explanation:

Ans.30 cm before the lens

Magnification M =-2 ( real and inverted image)

M = v / u =-2

V=-2u ....eq (1)

From lens formula

1/f = 1/v - 1/u .....eq (2)

Given f = 20cm

On substitution of eq (1) in (2) we get U = - 30 cm ( it is negative from the sign convention)