Question

The focal length of a concave mirror is $12cm$. Where should an object of length $4cm$ be placed, so that a real image of $1cm$ length is formed?

• A. $48cm$
• B. $3cm$
• C. $60cm$
• D. $15cm$

Answer 1

Answer: (C)

$60cm$

Given that,

Focal length of a concave mirror $f=12cm$

Object length $h=4$

Real image length $h^{\prime }=1cm$

We know that,

$m=-\frac{v}{u}=\frac{-f}{-f-\left(u\right)}$

$-\frac{1}{u}=\frac{-12}{-12-u}$

$12+u=-48$

$u=-48-12$

$u=-60cm$

Hence, the object distance is $60cm$