Question

A convex mirror has focal length of 20 cm and object is placed at a distance of 16 cm from it. The image distance is
a)15 cm b)8.9 cm c) -8.9 cm d) -15 cm​

Answer 1

Answer:

b) 8.9 cm

Explanation:

1/f = 1/v + 1/u

1/20 = 1 / v - 1 / 16

1/v = 1/20 + 1/16

    = 36 /320

v  =  8.9 cm

Answer 2

Given :-

Focal length (f) = 20cm

Object distance (u) = -16cm

Image distance (v) = ?

Solution :-

Mirror Formula :- 1/v + 1/u = 1/f

Or, 1/v = 1/f - 1/u

Substituting values in formula,

1/v = 1/20 - 1/(-16)

1/v = 1/20 + 1/16

1/v = (16 + 20)/(20 x 16)

1/v = 36/320

1/v = 9/80

9v = 80

v = 80/9

v = 8.9cm

∴ Image is formed 8.9cm behind the mirror.