Question

A man uses a concave mirror for shaving. He keeps his face at a distance of 25cm from the mirror and gets an image which is 1.4 times enlarged. Find the focal length of the mirror.

Answer 1

Given :

Object distance u= -25cm

m=1.4

m= -v/u

v= mx -u = 1.4 x 25 = 14x25/10 = 35 cm

From mirror equation :

1/f=1/v+1/u

1/f= 1/35 -1/25

= 5-7/135 = - 2/ 135

f= - 87.5cm

So focal length of concave mirror is 87. 5cm

Answer 2

$\textbf{Answer is in Attachment !}$