Class 12 Physics Wave Optics Wavefront

Wavefront

• Wave front is defined as locus of all points having same phase at a given instant of time.
• The shape of wavefront depends on the shape of the source of disturbance.
• A wavefront is always normal to the light rays.
• A wavefront does not propagate in the backward direction.

• There are 3 types of wavefronts:-
• Spherical wavefront(spherical in shape)
• Plane wavefront(linear in shape)
• Cylindrical wavefront(cylinder in shape)

Spherical Wavefront

• When the source of light is a point source the wavefront formed will be spherical wavefront.
• Point source means the source of light is so small that it is considered as point. It can be considered as dimensionless.
• For example: - Ripples in water are in the form of concentric circles which are spherical wavefronts.

Plane Wavefront

• When the small part of a spherical or cylindrical wavefront originates from a distant source like infinity then the wavefront which is obtained is known as plane wavefront.
• For example: -Rays coming from infinity like Sun.

Cylindrical Wavefront

• When the source of disturbance is a slit (i.e. line source) then the wavefront is cylindrical because all the points are equidistant from the source and they lie on the surface of the cylinder.
• For example: - In the figure we can see when rays of lightfall on a lens after coming out of lens, they will converge at a point.
• The waves are bending and converging at a point so the shape of the wavefront is in the form of cylinder.
• Many concentric circles are formed and the wavefront is in the form of cylinder.

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