Question

A 1 cm high object is placed at a distance of 32 cm from a concave mirror. The image is real, inverted and 1.5 cm in size. Calculate the focal length of the mirror and the position of the image. [3 MARKS]

Answer 1

Problem: 3 Marks

Given:

$u=-32cm$

$h_o=1cm$

$h_i=-1.5$

We know
$\frac{h_i}{h_o}=\frac{-v}{u}$

$\frac{-1.5}{1}=\frac{-v}{-32}$

$v=-48cm$

Image is 48 cm from the pole and on the same side of the object

Mirror formula $\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$

$\frac{1}{v}=\frac{1}{f}-\frac{1}{32}$

$f=-19.2cm$

Focal length of the mirror is 19.2 cm