Huygen was the first scientist who proposed the idea of wave theory...
0Huygen was the first scientist who proposed the idea of wave theory of light. He said that the light propagates in form of wavefronts. A wavefront is an imaginary surface at every point of which waves are in the same phase. For example the wavefronts for a point source of light is collection of concentric spheres which have centre at the origin. \( w_{1} \) is a wavefront. \( w_{2} \) is another wavefront. propagation of light is perpendicular to the surface of the wavefront. The wavefronts are plane wavefronts in case of a parallel beam of light.
Huygen also said that every point of the wavefront acts as the source of secondary wavelets. The tangent drawn to all secondary wavelets at a time is the new wavefront at that time. The wavelets are to be considered only in the forward direction (i.e. the direction of propagation of light) and not in the reverse direction. If a wavefront \( w_{1} \) at time \( t \) is given, then to draw the wavefront at time \( t+\Delta t \) take some points on the wavefront \( w_{1} \) and draw spheres of radius 'cAt'. They are called secondary wavelets.
Draw a surface \( w_{2} \) which is tangential to all these secondary wavelets. \( w_{2} \) is the wavefront at time \( '+\Delta t \) '. Huygen proved the laws of reflection and laws of refraction using concept of wavefronts.
Wavefronts incident on an interface between the media are shown in the figure. The refracted wavefronts will be as shown in
\( (\mathrm{A}) \)
(B)
(D)
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