Question

Time taken by light to cross a glass slab of thickness $4\, mm$ and refractive index $3$, is

• A. $ 4\times 10^{-11}s $
• B. $ 2\times 10^{-11}s $
• C. $ 16\times 10^{-11}s $
• D. $ 8\times 10^{-11}s $

Answer 1

Answer: (A)

Using the relation
Time taken $=\frac{\text { distance }}{\text { velocity }}$
$=\frac{\text { optical path }}{\text { velocity of light }}$
i.e. $t=\frac{\mu t}{c}=\frac{3 \times 4 \times 10^{-3}}{3 \times 10^{8}}$
$=4 \times 10^{-11} \sec$