Question

An object is placed at 60 cm from the pole of a concave mirror, whose focal length is 20 cm? Find the distance at which the image is formed.

• A. v = – 20 cm
• B. v = – 30 cm
• C. v = + 30 cm
• D. v = + 20 cm

Answer 1

Answer: (B), (C)

The correct options are
B

v = – 30 cm

C

v = + 30 cm

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

u = -60 cm, f = - 20 cm (using the sign conventions)

$\frac{1}{v}$ - $\frac{1}{60}$ = $\frac{-1}{20}$

$\frac{1}{v}$ = $\frac{-1}{30}$

v = - 30 cm (with sign convention)

i.e, v = 30 cm on the side of object