JEE MAIN - Physics (2024 - 30th January Morning Shift - No. 25)
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.
Odpověď
10
Vysvětlení
$$\begin{aligned}
& \frac{v}{u}=-2 \\
& v=-2 u \quad\text{... (i)} \\
& v-u=45 \quad\text{... (ii)}\\
& \Rightarrow u=-15 \mathrm{~cm} \\
& v=30 \mathrm{~cm} \\
& \frac{1}{f}=\frac{1}{v}-\frac{1}{u} \\
& f=+10 \mathrm{~cm}
\end{aligned}$$