Reflection of a light wave on a plane surface
To understand reflection of light on a plane surface in form of wave, let us consider wavefront AB incident on a plane surface making an angle 'i' with surface as shown in below figure.
In this figure, when wavenormal A is at point D, then wave B reaches at point O.As the both wave is in same medium their velocity is same. Let the velocity of wave is 'v' . After incident on the surface at D the wave startt forming next waveform in the same medium in forward direction and reaches point F in time 't' covering a distance DF= 'vt' and on the same time the wave at point O moves in forward direction and reaches point C covering a distance of OC = 'vt' in time 't' .
As wave travel in same medium thus distance covered by wave is given by DF = OC = vt.
Now according to huygens principle , the common tangent FC gives the next wave and thus reflection takes place.
Now In triangle DFC and Triangle DOC,
DC = DC --------------( Common side)
DF = OC ( Distance tarvelled in same time)
Angle DFC = Angle DOC --------( each 90)
thus Triangle DFC ∽ Triangle DOC
Angle ODC = Angle OCD -------(corresponding angle)
Angle i = Angle r
When reflection take place Angle i = Angle r
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