Question

The distance travelled by light in glass (refractive index $=1.5$) in a nanosecond will be

• A. $45cm$
• B. $40cm$
• C. $30cm$
• D. $20cm$

Answer 1

The correct option is D $20cm$

Refractive index of glass ${\mu }_g=\frac{3}{2}$
Speed of light in glass $c^{\prime }=\frac{c}{{\mu }_g}$
Distance travelled =$c^{\prime }t$
$t=1nanosecond=1\times {10}^{-9}s$
$Distance=\frac{c}{{\mu }_g}\times 1\times {10}^{-9}$
$=\frac{3\times {10}^8}{3/2}\times 1\times {10}^{-9}$
$=0.2m$
$=20cm$