Question

Describe the nature of image formed when the object is placed at a distance of 20 cm from a concave mirror of focal length 10 cm

Answer 1

Object distance (u) = - 20 m                           ( negative, due to sign convention)
Focal length (f) = -10 m                                   ( negative, due to sign convention)
Image distance = ?
From the mirror formula, we know that: 

`1/v+1/u=1/f` 

or `1/v+1/-20=(-1)/10` 

or `1/v-_20^1=_10^-1` 

or `1/v=(-1)/10+1/20` 

or `1/v=-1/20orv=-20m` 

Here, the negative sign means that the image is formed on the left side of the mirror. Thus, it is a real and inverted image, formed at a distance of 20 m from the mirror.