Question 284: Ray Optics

Question

The distance between object and its two times magnified real image as produced by a convex lens is $$45 \mathrm{~cm}$$. The focal length of the lens used is _______ cm.

Accepted Answer

$$\begin{aligned}
& \frac{v}{u}=-2 \
& v=-2 u \quad	ext{... (i)} \
& v-u=45 \quad	ext{... (ii)}\
& \Rightarrow u=-15 \mathrm{~cm} \
& v=30 \mathrm{~cm} \
& \frac{1}{f}=\frac{1}{v}-\frac{1}{u} \
& f=+10 \mathrm{~cm}
\end{aligned}$$

Ray Optics

The distance between object and its two times magnified real image as produced by a convex lens is $45 \mathrm{~cm}$. The focal length of the lens used is _______ cm.

Choose the correct answer: