An object is placed 5 cm from the pole of a concave mirror. If the focal length of the mirror is 10 cm. What is the image distance?

A. 10 cm in front of the mirror.
B. 5 cm in front of the mirror
C. 10 cm behind the mirror
D. 5 cm behind the mirror

Correct Answer:

Option C = 10 cm behind the mirror

Explanation

u = 5 cm , f = 10 cm, v = ?
(1)/v + (1)/u = (1)/f
(1)/v + (1)/5 = (1)/10
= (1)/v = (1)/10 = (1)/5 = (1 – 2)/10 = (1)/10
∴ v = – 10 cm
∴ The image is 10 cm behind the mirror