Question

Light of wavelength $500nm$ traveling with a speed of $2.0\times {10}^{8}m{s}^{-1}$ in a certain medium enters another medium of refractive index $5/4$ times that of the first medium. What are the wavelength and speed in the second medium?

• A. $400nm,1.6\times {10}^{8}m{s}^{-1}$
• B. $400nm,2.5\times {10}^{8}m{s}^{-1}$
• C. $500nm,2.5\times {10}^{8}m{s}^{-1}$
• D. $625nm,1.6\times {10}^{8}m{s}^{-1}$

Answer 1

The correct option is A $400nm,1.6\times {10}^{8}m{s}^{-1}$

Wavelength is ${\lambda }_m=\frac{{\lambda }_1}{n}=\frac{500}{5/4}=400nm$
Speed is $v_m=\frac{v_1}{n}=\frac{2\times {10}^8}{5/4}=1.6\times {10}^{8}m/s$
option $A$ is correct