Question

An object is kept at a distance of 5m in front of a spherical mirror, which forms its erect image at a distance of 2m from the mirror. What is the magnification? Is the mirror concave or convex?.​

Answer 1

u=-5 cm, f=10 cm

We know that

1/v + 1/u = 1/f

⇒ 1/v + 1/-5 = 1/10

⇒ 1/v = 1/20 + 1/5 = 3/10

∴v = 3/10 cm = 3.33 cm

The position of the image is 3.33 cm behind the convex mirror.

Magnification, m = – v/u = – 3.33/-5 =0.66

The image is virtual and erect.

Answer 2

u=4m

v=1m

m=-v/u

by sign convention, u=-4m

m=1/4 =0.2

∵ The magnification is positive and virtual diminished, the mirror could be convex.