Time taken by sunlight to pass through a window of thickness 8 mm and refractive index (3/2) is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 4\times10^{-11}\,\mathrm{s} \)
In a medium of refractive index n, light travels with speed \( v = c/n \), and the time to cross a thickness d is \( t = d/v \).
\( \displaystyle v = \frac{c}{n} = \frac{3\times10^{8}\,\mathrm{m\,s^{-1}}}{3/2} = 2\times10^{8}\,\mathrm{m\,s^{-1}} \)
\( d = 8\,\mathrm{mm} = 8\times10^{-3}\,\mathrm{m} \)
\( \displaystyle t = \frac{d}{v} = \frac{8\times10^{-3}\,\mathrm{m}}{2\times10^{8}\,\mathrm{m\,s^{-1}}} = 4\times10^{-11}\,\mathrm{s} \)