Question

An object of height 2.0 cm is placed at a distance 20 cm in front of a concave mirror of focal length 12 cm. Find the position, size and nature of the image.

Answer 1

u = -20 cm

f = -12 cm

h = 2 cm

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

$\frac{1}{v}$ = $\frac{1}{f}$ – $\frac{1}{u}$

$\frac{1}{v}$ = $\frac{1}{-12}$ – $\frac{1}{-20}$

$\frac{1}{v}$= $\frac{1}{20}$ – $\frac{1}{12}$

v = -30 cm

Image is real and is formed at a distance of 30 cm from the pole.

$\frac{h_i}{h_o}$= $\frac{-v}{u}$
$\frac{h_i}{u}$ = $\frac{30}{-20}$

$h_i$ = -3

Image is inverted and its size is 3 cm.