Solve the following question.

Question

A mirror forms an image which is 30 cm from an object and twice its height.

(a) Where must the mirror be situated?

(b) What is the radius of curvature?

(c) Is the mirror convex or concave?

Answer 1

Let the image formed is virtual and erect.

V – u = 30 cm

m = 2

(a) m = - (v/u)

2 = - (v/u)

V = -2u

-2u – u = 30 cm

u = -10 cm

(b) v = -2u = 20 cm

1/v + 1/u = 1/f

1/20 + 1/-10 = 1/f

1/f = -1/20

f = -20 cm

R = 2f = -40 cm

 Concave mirror