Question

Refractive index of glass with respect to the medium is $\frac{4}{3}$ . If the difference between velocities of light in medium and glass is $6.25 \, \times \, 10^{7 \, }m \, s^{- 1},$ then the velocity of light in medium is

• A. $2.5\times 10^{8 \, }m \, s^{- 1}$
• B. $0.125\times 10^{8} \, m \, s^{- 1}$
• C. $1.5\times 10^{8 \, }m \, s^{- 1}$
• D. $3\times 10^{8 \, }m \, s^{- 1}$

Answer 1

Answer: (A)

So, velocity of light in glass
$V_{g}=\frac{V_{m}}{\mu }$
$V_{m}-V_{g}=V_{m}-\frac{V_{m}}{\mu }$
$\therefore 6.25 \times 10^7=V_m\left(1-\frac{1}{\frac{4}{3}}\right)$
$V_{m}=6.25 \, \times 10^{7}\times 4$
$=2.5\times 10^{8} \, m \, s^{- 1}$