Question

9. When the distance of an object from concave mirror is
changed from 15 cm to 9 cm, then image formed becomes
three times magnified than the initial. Find the focal
length of the mirror.​

Answer 1

Explanation:

The relation between magnification,object distance and focal length is

m= f/ f-u

First case u = -15cm

m1= f/f+15

Second caseu= -9cm

m2= f/f+9

m2 = 3m1 , f/f+9 = 3 f/f+15

solving f= -6cm