Question

A candle flame of 0.5cm high is kept between wall and a concave mirror of focal length 1.5m such that it's image is 1.5cm high which is formed on the wall. Find the distance of candle from wall and also calculate the distance between wall and mirror.

Answer 1

Answer:

Distance between wall and the mirror = 6 cm

Distance of the candle from the wall = 4 cm

Explanation:

The distance between the wall and the mirror is the image distance as the image is formed on the wall.

f = - 1.5 cm

ho = 0.5 cm

hi = 1.5 cm

Magnification : m = hi /ho = - v /u

1.5 /0.5 = -v /u

3 = - v /u

-3 u = v

Lens formulae : 1 /v - 1 /u = 1 /f

-1 / 3u - 1 /u = - 1 /1.5  

-4 /3u = -1 /1.5

u = 2 cm

v = -6 cm

Distance of the candle from the wall = 6 - 2 = 4 cm