Class 12 Physics Wave Optics Examples for Refraction and reflection of plane waves

Examples for Refraction & reflection of plane waves

1. Prism:-
1. Consider when the light waves are coming from a source which is at infinity.
2. The wavefront will be plane wavefront.
3. When these wavefront passes through prism, the light waves and also the wavefront.
4. This shows the reflected wavefront.
2. Convex Lens(Converging Lens):-
1. Consider the incident wavefrontpassing through a convex lens.
2. The incident wavefront will converge at focus.
3. As the light rays changes its direction, the wavefront will also change as a result a curved wavefront is obtained.
3. Concave mirror:-
1. The concave mirror converges the incident wavefront at the focus which is at the same side.
• Effects ofPrism,convex lens and concave mirrorcan be explained in terms of wave front.
• According to Huygens velocity of the light in the denser medium is lesser than the velocity in the rarer medium.
• In a prism or convex lens, velocity of wavefront inside them is lesser than the velocity outside.
• Consider the fig the wave (1) will travel a very little portion of the denser medium whereas wave (2) will travel more portion of the rarer medium.
• This means the velocity of wave (2) is less for longer period of time because of which they take more time to come out of the prism.
• Wave (1) travel with lesser speed for small amount of time. So they reach faster.
• In case of convex lens the waves which are in middle will travel maximum portion of the denser medium. Therefore they travel more time in the denser medium.
• They have less velocity as a result they will take more time as compared to the waves at the edges.
• As the lens is thinner at both the edges. .