JEE PYQ: Ray Optics Question 28
Question 28 - 2020 (08 Jan Shift 1)
A point object in air is in front of the curved surface of a plano-convex lens. The radius of curvature of the curved surface is 30 cm and the refractive index of the lens material is 1.5, then the focal length of the lens (in cm) is __________.
Show Answer
Answer: (60)
Solution
Given: $\mu = 1.5$; $R_{\text{curved}} = 30$ cm Using, Lens-maker formula $\frac{1}{f} = (\mu - 1)\left(\frac{1}{R_1} - \frac{1}{R_2}\right)$ For plano-convex lens $R_1 \to \infty$ then $R_2 = -R$ $\therefore f = \frac{R}{\mu - 1} = \frac{30}{1.5 - 1} = 60$ cm
BETA
