Question

a student has to project a three times magnified image of a candle flame on a wall .name the type of the lens (converging or diverging) required for the purpose. if the candle flame is at a distance of 6 metre from the wall ,find the focal length of the lens.

Answer 1

the lens to be used is converging lens, ie;convex lens
Given
m=3m
u=-6m
v=?
m=v/u
therefore;v=mu
v=3×-6=-18m

1/f=1/v-1/u
=1/-18 - 1/-6
=-2/-18
therefore; f=-18/-2=9m