Question 7 - CBSE Class 12 Sample Paper for 2022 Boards [Term 2] - Physics - Solutions to CBSE Sample Paper - Physics Class 12

Define wavefront. Draw the shape of refracted wavefront when the plane incident wave undergoes refraction from optically denser medium to rarer medium. Hence prove Snell’s law of refraction. 

Answer

A locus of points in space which oscillate in the same phase is called a wavefront . 

That is, the phase difference between any two points of the same wavefront is zero .

Let us assume an incident wavefront AB incident on an interface between 2 media with refraction indices n1>n2.

According to Huygen’s wave theory:

• A source of light  gives out waves in all directions.
• Every point on the wavefront is a source of disturbance. These disturbances called secondary wavelets,  travel in all directions.
• The time taken by secondary wavelets to travel from primary to secondary wavefront is a constant . 

Therefore, on the basis on these statements we can say that: