Question

An object 5 cm high forms a virtual image of 1.25 cm high, when placed in front of a convex mirror at a distance of 24 cm. Calculate: (a) the position of the image, (b) the focal length of the convex mirror

Answer 1

Answer:

Height of object (h) = 5 cm.

Height of image (h' ) = 1.25 cm . ( positive because image is virtual and therefore erect )

Object distance (u) = - 24 cm.

M = h'/ h = -v/u

1.25/ 5= -v / - 24

0.25 = v / 24

v = 6 cm

By Mirror Formula

1/f = 1 /v + 1/ u

1/ f = 1/6 + 1 / - 24

1/f = 1/6 - 1 / 24

1/f = 4- 1 / 24

1 /f = 3/ 24

f = 24/3 = 8 cm