Question

what are Huygens principles?

Answer 1

The Huygens-Fresnel principle states that every point on a wavefront is a source of wavelets. These wavelets spread out in the forward direction, at the same speed as the source wave. The new wavefront is a line tangent to all of the wavelets.

Answer 2

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what are Huygens principles?

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$\Large\bold\green\star\underline{\underline\textbf{Use of Huygen's Principle\:}}$

Huygen's principle is used to find the position of the given wavefront at any instant of time, provided its present location is known.

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$\Large\bold\star\underline{\underline\textbf{Huygen's Principle\:}}$

According to this principle

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• Every point on the given wavefront acts as a source of new disturbance, called secondary wavelets which travel in all directions. The velocity of secondary wavelets is same as that of primary wavelets and is equal to velocity of light.

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• A tangent to the secondary wavelets in the forward direction at any instant gives the position of secondary wavefront at that instant.

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• In a homogeneous medium, the wavefront is alwavs normal to the direction of propagation of waves. Consider a primary wave front AB and take points 1, 2, 3, 4,--------- etc. on this wavefront. The distance travelled by light in 't' seconds= c x t, where c is the velocity of light. Now taking each point 1, 2, 3, 4,..... as centres and radius equal to c x 1, draw spheres. These spheres are called secondary wavelets. Now draw a tangent or envelope A1B1 to these spheres. The surface A2B2 is the position of secondary wavefront after 't' seconds .

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