Question

A three times magnified image of a candle flame is to be projected on a wall. Name the type of lens ( converging / diverging ) required for this purpose. If the candle flame is at a distance of 6m from the wall, calculate the focal length of the lens.

Answer 1

$$\begin{gathered} Dearstudent \\ \frac{-v}{u}=3\Rightarrow -v=3u......\left(1\right) \\ v+u=6.......\left(2\right) \\ -3u+u=6 \\ 2u=6 \\ u=3......\left(3\right) \\ \frac{1}{v}-\frac{1}{u}=\frac{1}{f} \\ -\frac{1}{3u}-\frac{1}{u}=\frac{1}{f}........\left(4\right) \\ -\frac{1}{3u}-\frac{3}{3u}=\frac{1}{f} \\ \frac{-4}{3\times 3}=\frac{1}{f} \\ f=\frac{9}{4}m \\ Regards \end{gathered}$$