Question

An object is placed at 60 m in front of a concave mirror. If its radius of curvature is 40 m, then the image distance is

• A. 20
• B. 30
• C. 60
• D. 120

Answer 1

The correct option is B

30

Using Mirror Formula
Sign conventions for u = -ve ( Left side of the mirror)
f = -ve ( Concave mirror)
$\frac{1}{v}$ + $\frac{1}{u}$ = $\frac{1}{f}$
$\frac{1}{v}$ + $\frac{1}{-60}$ = $\frac{-1}{20}$

$\frac{1}{v}$ = $\frac{1-3}{60}$

v= -30m
Negative sign represents that object and image are on the same side of mirror.