Question

We wish to obtain an equal sized inverted image of a candle flame on a screen kept at distance of 4 m from the candle flame. (a) Name the type of lens that should be used. (b) What should be the focal length of the lens and at what distance from the candle flame the lens be placed. (c) Draw a labelled diagram to show the image formation in this case..

Answer 1

(a) convex lens should be used

(b) u+v=4m
u=v
so u=v=2m
using lens formula
$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
$\frac{1}{f} = \frac{1}{2} - ( - \frac{1}{2} ) \\ \frac{1}{f} = 1 \\ f = 1m$

Answer 2

Whaen experimenting the reflexive properties of light using a convex lens we observe that the nature of the image formed depends entirely on the distance of the object which in this case is the candle

When the focal length is longer then the image formed is real and equal sized and inverted