Question

The time taken by a ray of light to travel through a glass slab of thickness $2mm$ and refractive index $1.5$ will be

• A. ${10}^{-8}$
• B. ${10}^{-10}$
• C. $2\times {10}^{-8}$
• D. ${10}^{-12}$

Answer 1

Answer: (B)

${10}^{-10}$

Given, refractive index of glass

${\mu }_g=1.5$

We know,

$\mu =\frac{Speedoflightinvacuum}{Speedoflightinmedium}=\frac{c}{v}$

$\Rightarrow v=\frac{c}{{\mu }_g}$

$\Rightarrow v=\frac{3\times {10}^8}{1.5}=2\times {10}^{8}m{s}^{-1}$

Thickness of the slab, $d=2cm=0.02m$

Time taken by a ray of light to travel through the glass slab is given as

$t=\frac{d}{v}=\frac{0.02}{2\times {10}^8}={10}^{-10}seconds$

Hence, the correct answer is OPTION B.