Chapter 14, Problem 75A

To determine

The two changes and what does not change when the wave fronts pass from one medium to another at different speed.

Explanation of Solution

Introduction:

That virtual surface over which the optical waves have constant phase known as wave front.

With the help of the geometry of the source the shape of the wave front can be determined.

According to the Huygens’s principle:

1. Each and every point on the wave front acts as the new source of the secondary wavelets which propagates with the speed of light in all directions.
2. At any instant a new wave front gets rise by the forward envelope of these secondary waves

Changes occur when the wave fronts pass from one medium to another medium. There is change in velocity give rise to change in wavelength according to the relation given below:

  $\lambda =\frac{v}{f}$

Where,

  $\lambda$ is the wavelength

  $v$ is the velocity

  $f$ is the frequency

Also, there is the change in the direction in which the wave frontpasses. The frequency of wavefront remains same; no changes occur in the frequency of wavefront.

The speed of the waves becomes slow and the wavelength starts getting short and ultimately the frequency remains same.

Conclusion:

When wave front passes at angle from one medium to another, frequency of wave does not change. But its velocity and wavelength changes.