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.
Answer (integer)
10
Solution
<p>$$\begin{aligned}
& \frac{v}{u}=-2 \\
& v=-2 u \quad\text{... (i)} \\
& v-u=45 \quad\text{... (ii)}\\
& \Rightarrow u=-15 \mathrm{~cm} \\
& v=30 \mathrm{~cm} \\
& \frac{1}{f}=\frac{1}{v}-\frac{1}{u} \\
& f=+10 \mathrm{~cm}
\end{aligned}$$</p>
About this question
Subject: Physics · Chapter: Optics · Topic: Lenses and Optical Instruments
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