Question

An object 50cm tall is placed on the principal axis of a convex lens.its 20 cm image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens

Answer 1

hey

magnification(m) = hi/ho

m = 20/50

m = 2/5

2/5 = 10/u

u = 50/2

u = 25cm

by using lens formula ,

1/f = 1/v - 1/u

1/f = 1/-10 - 1/25

1/f = -5 - 2 / 50

1/f = -7/50

f = 50/-7

f = - 7.1cm