Question

A candle flame 3 cm is placed at distance of 3 m from a wall. How far from wall must a concave mirror be placed in order that it may form an image of flame 9 cm high on the wall

• A. 225 cm
• B. 300 cm
• C. 450 cm
• D. 650 cm

Answer 1

The correct option is C 450 cm

Let the mirror be placed at a distance x from wall
By using
$\frac{I}{O}=\frac{-v}{u}\Rightarrow \frac{-9}{+3}=\frac{-(-x)}{-(x-3)}$

$9(x-3)=3x$

$3x-9=x$

$2x=9$

$\Rightarrow x=4.5m=450cm$.