Question

A square wire of side $1\,cm$ is placed perpendicular to the principal axis of a concave mirror of focal length $15\,cm$ at a distance of $20 \,cm$. The area enclosed by the image of the wire is

• A. $ 4c{{m}^{2}} $
• B. $ 6c{{m}^{2}} $
• C. $ 2c{{m}^{2}} $
• D. $ 8c{{m}^{2}} $
• E. $ 9c{{m}^{2}} $

Answer 1

Answer: (E)

Given focal length of concave mirror
$ f=-15cm $ $ u=-20\text{ }cm $
Magnification $ m=\frac{f}{u-f} $
$ =\frac{-15}{-20+15} $
$ m=3\,cm $
The area enclosed by the image of the wire
$ ={{m}^{2}} $ $ =9\text{ }cm $