Question

Light of wavelength $5000\AA$ falls on a plane reflecting surface. What are the wavelength and frequency of the reflected light? For what angle of incidence is the reflected ray normal to the incident ray?

Answer 1

Given,
Light of wavelength $\lambda =5000\AA$
As frequency is the property of source it remains unchanged if light propagates through any medium.
$c=v\lambda$
$v=\frac{3\times {10}^8}{5000\times {10}^{-10}}$
$v=6\times {10}^{14}\text{Hz}$
The wavelength and frequancy of the reflected ray will be same as the incident ray.

From law of reflection,
$\angle i=\angle r$

Given,
$i+r={90}^{\circ }$
$2i={90}^{\circ }$
$i={45}^{\circ }$
Final Answer: $5000\AA ,6\times {10}^{14}\text{Hz},{45}^{\circ }$.