Question

An object placed 20 cm from a convex mirror its image is formed 12 cm from the mirror find foacal length

Answer 1

Given :

Distance of object = 20cm

Distance of image = 12cm

Type of mirror : convex

To Find :

Focal length of the mirror.

Solution :

✵ Focal length of convex mirror is taken positive and that of concave mirror is taken negative.

For convex mirror, image is formed behing the reflecting surface.

Focal length of mirror can be calculated by using mirror formula which is given by

$\bigstar\:\underline{\boxed{\bf{\purple{\dfrac{1}{u}+\dfrac{1}{v}=\dfrac{1}{f}}}}}$

u denotes distance of object

v denotes distance of image

f denotes focal length

By substituting the given values;

$:\implies\sf\:\dfrac{1}{-20}+\dfrac{1}{12}=\dfrac{1}{f}$

$:\implies\sf\:\dfrac{-3+5}{60}=\dfrac{1}{f}$

$:\implies\sf\:\dfrac{2}{60}=\dfrac{1}{f}$

$:\implies\:\underline{\boxed{\bf{\orange{f=30\:cm}}}}$