Question

An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focused image can be obtained? Find the size and the nature of the image.

Answer 1

Object distance, u= – 27 cm
Object height, h= 7 cm
Focal length, f = – 18 cm
According to the mirror formula,

`1/v-1/u=1/f`

`1/v=1/f-1/u=-1/18+1/27=-1/54`

`v=-54 cm`

The screen should be placed at a distance of 54 cm in front of the given mirror.

`h_1/h=-v/u`

The negative value of magnification indicates that the image formed is real.

`h_1/7=-54/27`

h₁=7 x (-2)= -14 cm

The negative value of image height indicates that the image formed is inverted.