Question

Light travels with a speed of $2 \times 10^{8} \,m / s$ in crown glass of refractive index $1.5$. What is the speed of light in dense flint glass of refractive index $1.8 ?$

• A. $1.33 \times 10^{8}\, m / s$
• B. $67 \times 10^{8} \,m / s$
• C. $2.0 \times 10^{8} \,m / s$
• D. $3.0 \times 10^{8}\, m / s$

Answer 1

Answer: (B)

$\mu=\frac{c}{v}$
$\therefore \frac{\mu}{\mu^{'}}=\frac{v^{'}}{v}$
$\frac{1.5}{1.8} =\frac{v^{'}}{2 \times 10^{8}} $
$ v^{'} =\frac{3 \times 10^{8}}{1.8} $
$=1.67 \times 10^{8} \,m / s$