JEE PYQ: Ray Optics Question 2
Question 2 - 2021 (16 Mar Shift 2)
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)
(1) 1
(2) Infinite
(3) $\frac{R_1 R_2}{R_1 - R_2}$
(4) Zero
Show Answer
Answer: (2)
Solution
$\frac{1}{F} = \left(\frac{\mu_L}{\mu_S} - 1\right)\left[\frac{1}{R_1} - \frac{1}{R_2}\right]$ If $\mu_L = \mu_S \Rightarrow \frac{1}{F} = 0 \Rightarrow F = \infty$
BETA
