Q. The time required for the light to pass through a glass slab (refractive index =1.5) of thickness 4mm is…$(c = 3 \times 10⁸\ \ {ms}^{- 1},$speed of light in free space).
A) $2\ \times \ 10^{- 5}\ s$
B) $2 \times \ 10^{11}\ s$
C) $2 \times \ 10^{- 11}\ s$
D) $10^{- 11}s$
Explanation
(c) $\frac{n_{g}}{n_{a}} = \frac{c_{a}}{c_{g}}$
$\frac{3}{2} = \frac{{3 \times 10}^{8}}{c_{g}}$
$c_{g} = 2 \times 10^{8}$
$Time = \frac{Distance}{Speed}$
$\ \ \ \ \ \ \ \ \ \ \ = \frac{4 \times 10^{- 3}}{2 \times 10^{8}} = 2 \times 10^{- 11}s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.