What will be the time by light to travel 2 cm thickness of glass of refractive index 1.5?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( 10^{-10}\,\mathrm{s} \)
Light travels slower in glass: its speed is the speed in vacuum divided by the refractive index, \( v = c/n \). The time is the thickness divided by this speed.
\( \displaystyle t = \frac{d}{v} = \frac{n\,d}{c} \)
\( d = 2\,\mathrm{cm} = 2\times10^{-2}\,\mathrm{m} \)
\( c = 3\times10^{8}\,\mathrm{m\,s^{-1}} \)
\( \displaystyle t = \frac{1.5 \times 2\times10^{-2}}{3\times10^{8}} = \frac{3\times10^{-2}}{3\times10^{8}} = 10^{-10}\,\mathrm{s} \)