CBSE Class 12 Sample Paper for 2022 Boards [Term 2] - Physics

Physics Class 12
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.

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:

### Transcript

Question 7 Define wavefront. Draw the shape of refracted wavefront when the plane incident wave undergoes refraction from optically denser medium to rarer medium. Hence prove Snellβs law of refraction. The time taken by the wavefront to travel Distance BC and AE in the same π‘_π΅πΆ=π‘_π΄πΈ If the velocity of the wave front in medium 1 and 2 is π£_1 and π£_2 π‘_π΅πΆ=π‘_π΄πΈ π΅πΆ/π£_1 = π΄πΈ/π£_2 π΅πΆ/(π/π_1 )=π΄πΈ/(π/π_2 ) γ(πγ_1) π΅πΆ=γ(πγ_2) π΄πΈ π_1/π_2 =π΄πΈ/π΅πΆ Now, sinβ‘π=π΅πΆ/π΄πΆ, sinβ‘π=π΄πΈ/π΄πΆ sinβ‘π/sinβ‘π = ((π΄πΈ/π΄πΆ))/((π΅πΆ/π΄πΆ) )=π΄πΈ/π΅πΆ=π_1/π_2 sinβ‘π/sinβ‘π =π_1/π_2 π_2 sinβ‘π=π_1 sinβ‘π Or π_1 sinβ‘π=π_2 sinβ‘π Hence, snells law is proved using huygenβs wave theory.