Question

In a car, a rearview mirror having a radius of curvature of 20 m forms a virtual image of a bus 5 m behind the mirror. What is the actual distance of the bus from the car?

[0.8 mark]

• A. 10 m
• B. 20 m
• C. 5 m
• D. 5/3 m

Answer 1

The correct option is A 10 m

We know that,
Radius of curvature, R = 2f
(where f is the focal length)
Therefore,
$f=\frac{+20}{2}$ = +$10m$
(Rearview mirror uses convex mirror)

Using mirror formula,
$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$
$\frac{1}{10}=\frac{1}{5}+\frac{1}{u}$
$u=-10m$
Hence, the bus is actually 10 m away from the car.