Question

For a colour of light the wavelength for air is $6000\,\mathring{A}$ and in water the wavelength is$4500\,\mathring{A}$. Then the speed of light in water will be

• A. $5 \times 10^{14} m / s$
• B. $2.25 \times 10^{8} m / s$
• C. $4.0 \times 10^{8} m / s$
• D. zero

Answer 1

Answer: (B)

We know that $v \propto \lambda$
$\Rightarrow \frac{v_{1}}{v_{2}}=\frac{\lambda_{1}}{\lambda_{2}}$
$\Rightarrow v_{2}=\frac{v_{1}}{\lambda_{1}} \times \lambda_{2}$
$=3 \times 10^{8} \times \frac{4500}{6000}=2.25 \times 10^{8} m / s$