Question

An object is placed 10 cm from a convex mirror. Its image is formed 15 cm behind the mirror.The focal length of the given convex mirror is

Answer: The focal length of the given convex mirror can be obtained using the mirror formula. It is given as:

Where,Object distance, u = 10 cm

Image distance, v = 15 cm

Focal length = fTherefore, f = 30 cm

Hence, the focal length of the given convex mirror is 30 cm

HOWCANTHEFOCALLENGTHOF

CONVEXMIRRORBNEGATIVE

Answer 1

Here,
Object distance, u=-10 cm
Image distance, v=+15 cm
Focal length, f=?
Using mirror formula,
1/f= 1/v + 1/u
=1/15 + 1/(-10)
=1/15-1/10
f= -30 cm
As the focal length is negative it means the mirror must be a concave mirror. A virtual image is produced when the object lies between the focus and the pole of the mirror.