Ray Optics And Optical Instruments Ques 2
2. A plano-convex lens is made of material of refractive index 1.6. The radius of curvature of the curved surface is $60 $ $\mathrm{cm}$. The focal length of the lens is
[1999]
(a) $50 $ $\mathrm{cm}$
(b) $100 $ $\mathrm{cm}$
(c) $200$ $ \mathrm{cm}$
(d) $400$ $ \mathrm{cm}$
Show Answer
Answer:
Correct Answer: 2.(b)
Solution: (b) $ R_1=60 \mathrm{cm}, R_2=\infty, \mu=1.6 $
$ \frac{1}{f}=(\mu-1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right) $
$\frac{1}{f}=(1.6-1)\left(\frac{1}{60}\right) \Rightarrow f=100 $ $\mathrm{cm} .$
BETA
