Question

Two identical pointed particles a and b are placed in front of a concave mirror of focal length 20 cm and distances 10cm and 30cm respectively the particles oscillate perpendicular to the principal axis

Answer 1

Given that,

Focal length = 20 cm

Distance of particle a = 10 cm

Distance of particle b = 30 cm

Suppose find the image distance of both particle

We need to calculate the image distance of particle a

Using formula of mirror

$\dfrac{1}{f}=\dfrac{1}{v}+\dfrac{1}{u}$

Put the value into the formula

$\dfrac{1}{-20}=\dfrac{1}{v}+\dfrac{1}{-10}$

$\dfrac{1}{v}=\dfrac{1}{-20}+\dfrac{1}{10}$

$\dfrac{1}{v}=\dfrac{1}{20}$

$v=20\ cm$

We need to calculate the image distance of particle b

Using formula of mirror

$\dfrac{1}{f}=\dfrac{1}{v}+\dfrac{1}{u}$

Put the value into the formula

$\dfrac{1}{-20}=\dfrac{1}{v}+\dfrac{1}{-30}$

$\dfrac{1}{v}=\dfrac{1}{-20}+\dfrac{1}{30}$

$\dfrac{1}{v}=\dfrac{1}{-60}$

$v=-60\ cm$

Hence, The image distance of particle a is 20 cm the image of a is formed at back of mirror.

The image distance of particle b is 60 cm and the image of b is formed at front of mirror.