Question

A light of wavelength $6000A^o$ in the air enters a medium of refractive index $1.5$. Inside the medium, its frequency is $\nu$ its wavelength is $\lambda$.Then find which is correct among the following.

• A. $v=5\times {10}^{14}{H}_z$
• B. $v=7.5\times {10}^{14}{H}_z$
• C. $\lambda =4000A^0$
• D. $\lambda =9000A^o$

Answer 1

Answer: (A), (C)

The correct options are
A $v=5\times {10}^{14}{H}_z$
C $\lambda =4000A^0$

As the light enters in the medium from air, its wavelength and velocity decreases, but frequency remains constant. So lets calculate the frequency of light in air.
We know:
$v=(\nu \times \lambda )$
Substituting values we get,

$\nu =\frac{3\times {10}^8}{6000\times {10}^{-10}}$

Frequency , $\nu =5\times {10}^{14}Hz$ (Option A)
As, $\mu =\frac{c}{\lambda }$

$\frac{\mu }{{\mu }^{\prime }}=\frac{{\lambda }^{\prime }}{\lambda }$

$\lambda =\frac{6000\times {10}^{-10}}{1.5}$

$=4000\mathring{A}$