Question:
The refractive index of a converging lens is $1.4$. What will be the focal length of this lens if it is placed in a medium of same refractive index ?
(Assume the radii of curvature of the faces of lens are $R_{1}$ and $R_{2}$ respectively)
Correct Option: , 2
Solution:
(2)
$\frac{1}{\mathrm{~F}}=\left[\frac{\mu_{\mathrm{L}}}{\mu_{\mathrm{s}}}-1\right]\left[\frac{1}{\mathrm{R}_{1}}-\frac{1}{\mathrm{R}_{2}}\right]$
If $\mu_{\mathrm{L}}=\mu_{\mathrm{S}} \Rightarrow \frac{1}{\mathrm{~F}}=0 \Rightarrow \mathrm{F}=\infty$