Question

An object is placed at a distance of $30cm$ from a concave mirror of focal length $20cm$, then nature and magnification of the image will be:

• A. $\text{Real},-2$
• B. $\text{Apparent},-2$
• C. $\text{Real},+2$
• D. $\text{Apparent},+2$

Answer 1

The correct option is A $\text{Real},-2$

Given,

focal length, $f=-20cm$

image distance, $u=-30cm$

object distance, $v=?$

Using mirror formula,
$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$
$\frac{1}{v}+\frac{1}{-30}=\frac{1}{-20}$
or $\frac{1}{v}=-\frac{1}{20}+\frac{1}{30}=\frac{-3+2}{60}=-\frac{1}{60}$
$\therefore v=-60cm$ (real image)
$\therefore$ Magnification, $m=-\frac{v}{u}=-\frac{-60}{-30}=-2$
or $m=-2$