Question

The refractive index of glass is 1.5 and velocity of light in vacuum is 3$\times$ 10${}^8$ m/s. Time taken by light in traveling 500 m in glass will be:

• A. $1\mu s$
• B. $1.5\mu s$
• C. $4.5\mu s$
• D. $2.5\mu s$

Answer 1

Answer: (D)

Given,$n_g=1.5,n_{vacuum}=1$ and velocity of light in vacuum is $3\times {10}^8$.
Velocity of light in glass is :
$\frac{v_v\times n_v}{n_g}$
$=\frac{3\times {10}^8\times 1}{1.5}$
$=2\times {10}^8.$
Therefore, time taken by light in travelling 500m in glass is $\frac{500}{2\times {10}^8}$
$=2.5\mu s$