10. Time taken by sunlight to pass through a window of thickness 4 mm whose refractive index is 3/2 is ?

10. Time taken by sunlight to pass through a window of thickness 4 mm whose refractive index is 3/2 is ?

(a) \( 2 \times 10^{-4} \, \text{sec} \)

(b) \( 2 \times 10^{8} \, \text{sec} \)

(c) \( 2 \times 10^{-11} \, \text{sec} \)

(d) \( 2 \times 10^{11} \, \text{sec} \)

Answer :  (c) \( 2 \times 10^{-11} \, \text{sec} \)

\( \mu = \frac{c}{v} \)

\( \Rightarrow \, v = \frac{c}{\mu} \)

\( v = \frac{d}{t} \)

\( \Rightarrow \, t = \frac{d}{v} \)

\( = \frac{4 \times 10^{-3}}{\frac{3 \times 10^8}{\frac{3}{2}}} \)

\( = \frac{4 \times 10^{-3}}{2 \times 10^8} \)

\( = 2 \times 10^{-11} \, \text{sec} \)