Question

An object is placed in front of a concave mirror of focal length 20cm. The image formed is 3 times the size of the object. Calculate two possible distances of the object from the mirror​

Answer 1

Answer:

(a) 80/3 cm

(b) -40/3 cm

Explanation:

Given that, image size is 3 times object size. Thus magnification is ±3.

(a) For M = +3,

v/u = +3

v = 3u

Using mirror formula,

1/f = 1/v + 1/u

1/20 = 1/3u + 1/u

Solving this,

u = 80/3 cm

(b) For M = -3,

v/u = -3

v = -3u

Using mirror formula,

1/f = 1/v + 1/u

1/20 = 1/-3u + 1/u

Solving this,

u = -40/3 cm

Hope it helps!!