Question

Q.5- The image of a candle flame placed at a distance of 30 cm from a mirror is formed on a screen placed in front of the mirror at a distance of 60 cm from its pole. What is the nature of the mirror? Find its focal length.

Answer 1

THE NATURE OF MIRROR IS CONCAVE AS THE IMAGE IS FORMED ON A SCREEN WHICH COMES UNDER REAL IMAGE AND CONCAVE MIRROR FORMS REAL IMAGES.SO THE MIRROR WILL BE CONCAVE.

THE FOCAL LENGTH OF MIRROR IS

1/f=1/v + 1/u

as v= -60cm , u= -30cm and f=-x(by sign scheme)

-1/f=-(1/60+1/30)

cancelling minus on both sides

1/f=3/60(by foing lcm of two fractions)

this gives

1/f =1/20

by rearranging

f=-20cm(by sign scheme)

HOPE THIS HELPS