Ray Optics And Optical Instruments Ques 20
20. Time taken by sunlight to pass through a window of thickness $4$ $ mm$ whose refractive index is $\frac{3}{2}$ is
(a) $2 \times 10^{-4} $ $sec$
(b) $2 \times 10^{8} $ $sec$
(c) $2 \times 10^{-11} $ $sec$
(d) $2 \times 10^{11} $ $sec$
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Answer:
Correct Answer: 20.(c)
Solution:
- (c) $v_g=\frac{c}{\mu}=\frac{3 \times 10^{8}}{\frac{3}{2}}=2 \times 10^{8}$ $ m / s$
$t=\frac{x}{v_g}=\frac{4 \times 10^{-3}}{2 \times 10^{8}}=2 \times 10^{-11} $ $s$
BETA
