Question

A concave mirror is made from a hollow sphere of radius of curvature $30cm$. If an object of height $2cm$ is placed at $10cm$ from the pole of the mirror, determine the size of the image :

• A. $3cm$
• B. $6cm$
• C. $12cm$
• D. $24cm$

Answer 1

The correct option is B $6cm$

Given:

$u=-10cm$

$f=-15cm$

$h_o=+2cm$

To find, $h_i$

From mirror formula,

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

$\Rightarrow \frac{1}{v}-\frac{1}{10}=-\frac{1}{15}$

$\Rightarrow \frac{1}{v}=\frac{1}{10}-\frac{1}{15}=\frac{5}{150}$

$v=+30cm$

$magnification=\frac{h_i}{h_o}=\frac{-v}{u}$

$\frac{h_i}{+2}=\frac{-30}{-10}$

$h_i=+6cm$