Question

An object is placed at $60m$ in front of a concave mirror. If its radius of curvature is $40m$, then find the image distance.[3 marks]

Answer 1

Given, distance of the object from the mirror, u=−60 m (object is on the left side of the mirror) and radius of curvature, R=40 m
We know, focal length, f=$\frac{R}{2}$=$\frac{40}{2}$ =20 m
For concave mirror, f is negative, i.e f=−20 m
Let the image distance be v.

Using mirror formula
$\frac{1}{v}$+$\frac{1}{u}$=$\frac{1}{f}$
$\frac{1}{v}$+$\frac{1}{-60}$=$\frac{1}{-20}$
v=-30m [3 Marks]