Question

A candle is sitting in front of a concave mirror at a distance of 12.2 cm. It is found that an image of the candle appears at 25.0 cm. What is the focal length of the mirror?

3.52 cm
8.20 cm
10.4 cm
22.1 cm

Answer 1

It would be b. 8.20cm

Answer 2

8.20cm

Step-by-step explanation:

We use the formula:


`(1)/(i)+(1)/(o) =(1)/(f)`

Where i- image distance ; o - object distance ; f - focal length

=1/25 +1/12.2

=0.121

We take reciprocal of this as it is 1/f to find 'f'

=1/0.121

=8.20cm (2dp)