Question

A boy stands straight in front of a mirror at a distance $30cm$ away from it. He sees his erect image whose height is ${\left(\frac{1}{5}\right)}^{th}$ of his real height. The mirror he is using is :

• A. plane mirror
• B. convex mirror
• C. concave mirror
• D. plano-concave mirror

Answer 1

Answer: (B)

convex mirror

Only a convex mirror can produce an erect, virtual and diminished image of an object because in question it is given height of image is $\frac{1}{5}$th of real height.

$\frac{-v}{u}=M<1$

$⟹v<-u$

$⟹\frac{1}{v}>-\frac{1}{u}$

$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$
$⟹\frac{1}{f}>\frac{1}{-u}+\frac{1}{u}>0$

$⟹f>0$

$⟹$ Convex mirror