Question

An object is kept perpendicular to the principal axis of a convex mirror of radius of curvature 20 cm . If the distance of the object from mirror is 20 cm then its magnification will be :

• A. +1/3
• B. -1/3
• C. -1
• D. None of these

Answer 1

The correct option is A +1/3

We have,

From mirror formula, $\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$

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

$\frac{1}{v}=\frac{3}{20}$

$\therefore v=\frac{20}{3}$

Magnification,

$m=\frac{-v}{u}$

$=\frac{\frac{-20}{3}}{-20}$

$\therefore m=\frac{1}{3}$