Question

A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.

Answer 1

Height of object, h = 4.5 cm, u = – 12 cm.

f = 15 cm, v = ? m = ?

1/v = 1/f - 1/u = 1/15 - 1/(-12) = 1/15 + 1/12

⇒ 1/v = (4 + 5)/60 = 9/60

∴ v = 60/9 = 6.7 cm.

m = h'/h = c/u

∴ h' = v/u x h = -(6.7/-12) x 4.5 = 2.5 cm.

The image is virtual and *****. As the needle is moved farther from the mirror, the image moves away from the mirror