Question

An object of 50 cm tall is placed on the principal axis of a convex lens. Its 20cm tall image is formed on

the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens. A concave

lens has focal length 20cm.​

Answer 1

Explanation:

given,

height of image= 50

u= -20cm

v= 10cm

therefore,

1/f= 1/v+ 1/u

1/f= 1/10+1/-20

1/f= 2-1/20

1/f=1/20

f= 20cm