Question

An object of $5cm$ is placed before a concave mirror at a distance of $40cm.$ If its focal length is $20cm$ then what is the magnification of the image.

• A. $40$
• B. $20$
• C. $5$
• D. $-1$

Answer 1

The correct option is D $-1$

$\begin{array}{c}\frac{1}{v}=\frac{1}{t}-\frac{1}{u}\\ =\frac{-1}{20}-\frac{1}{-40}=\frac{-1}{40}\\ v=-40\\ m=-\frac{v}{u}=-\frac{-40}{-40}=-1\\ \therefore 1\times 1=1\\ Ans.\left(D\right)\end{array}$