An object is kept in front of a convex mirror of focal length 30 cm. The image formed is one fourth of the object size. What is the distance of the image from the mirror?

Answer 1

For a convex mirror, focal length is a negative number, f = -20 cm. With the mirror equation 1/d_o + 1/d_i = 1/f and object distance d_o = 4 d_i, 1/4d_i + 1/d_i = - 1/30 = (1 + 4) / 4d_i using common denominator. Flip this to get -30 = 4d_i /5 and image distance d_i = - 37.5 cm behind the mirror.