Question

A concave mirror of radius of curvature 30 cm produces a real image 3 times the size of an object. Find object distance?

Answer 1

Given :

Radius of curvature = 30cm

Image size = 3 times

To find:

The distance between object and image.

Solution :

As radius of curvature of concave mirror is 30cm

therefore, focal length of concave mirror, f = -R/2 = -30/2 = -15 cm

As real image is three times the size of the object,

thus magnification, m = - 3

= -v/u = -3

= v = 3u --- eq 1

Lens formula, 1/v + 1/u = 1/f

= 1/3u + 1/u = 1/-15

= 4/3u = 1/-15

= u = - 20 cm

v = 3u = 3 × -20

= - 60

Distance between the object and the image 60 - 20 = 40

Answer: The object distance is 40cm