JEE Advanced 2024 — Paper 1 — Question 24

$\quad \frac{1}{f}=(n-1)\left(\frac{1}{R_{1}}-\frac{1}{R_{2}}\right)$

$\frac{1}{f}=(1.6-1)\left(\frac{1}{9}-\frac{1}{\infty}\right)$

$f_{1}=\frac{9}{0.6}=15 \mathrm{~cm}$

$\frac{1}{f_{2}}=(n-1)\left(\frac{1}{\infty}-\frac{1}{9}\right)$

$\mathrm{f}_{2}=\frac{-9}{(\mathrm{n}-1)}$

$\mathrm{P}=2 \mathrm{P}_{1}+2 \mathrm{P}_{2}$

$\frac{1}{f_{\text {eq }}}=\frac{2}{15}-\frac{2(\mathrm{n}-1)}{9}$

$\frac{1}{f_{\text {eq }}}=\frac{18-2(\mathrm{n}-1) \times 15}{15 \times 9}$

$f_{\text {eq }}=\frac{15 \times 9}{18-2(n-1) \times 15}$

Image $\mathrm{V}=\mathrm{R}=2 \mathrm{f}_{\mathrm{e}}=\frac{2 \times 15 \times 9}{18-2(\mathrm{n}-1) \times 15}$