Q. For a colour of light the wavelength for air is $6000\ \mathring{\mathrm{A}}$ and in water the wavelength is $4500\ \mathring{\mathrm{A}}$. Then the speed of light in water will be
A) $5.0 \times 10^{14}\ m/s$
B) $2.25 \times 10^{8}\ m/s$
C) $4.0 \times 10^{8}\ m/s$
D) Zero
Explanation
(b) $v \propto \lambda \Rightarrow \frac{v_{1}}{v_{2}} = \frac{\lambda_{1}}{\lambda_{2}}$
$\therefore v_{2} = \frac{v_{1}}{\lambda_{1}} \times \lambda_{2} = 3 \times 10^{8} \times \frac{4500}{6000} = 2.25 \times 10^{8}m/s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.