Question

A concave mirror forms an image of 20 cm high object on a screen placed 5.0 m away from the mirror. The height of the image is 50 cm. Find the focal length of the mirror and the distance between the mirror and the object.

Answer 1

Correct Answer - A::B::C::D
Given that `h_1=20 dm`
v=-5m=-500cm`
`since (-v)/u=h_2/h_1`
or `500/u=50/20`
(becau7se the image is inverted)
`or y=-500xx2/5`
=`200cm=-2m`
`1/v+1/u=1/f`
or `1/(-5)+1/(-2)=1/f`
or `-1/f=7/10`
or f=-10/7=-1.44`
`so the focal length is 1.44 m.