Define the term wavefront. Using Huygens' wave theory, verify the laws of reflection.

Explanation

Let a plane wavefront ABC be incident from medium 1 on the plane surface AGF. At t= 0, the wavefront just touches the surface at A and sends wavelet travelling with a velocity `c_(1)` in medium 1 and with a velocity `c_(2)` in medium 2.

After time interval t, the wave travels the distance CF= `c_(1)t` and during which the secondary waves from A travel a distance `AD = c_(2)t`. If `angleCAF=i and angleAFD=r`, where i and r are the angle of incidence and the angle of refraction. Consider `DeltaACF and DeltaADF`, then we have
`sin i= sin angleCAF`
`= (CF)/(AF)= (c_(1)t)/(AF)`
and `sin r= sin angleAFD`
`=(AD)/(AF)= (c_(2)t)/(AF)`
`therefore (sin i)/(sin r)= ((c_(1) t)/(AF))/((c_(2)t)/(AF))= (c_(1))/(c_(2))`
`=""_(1)n_(2)`= a constant
`""_(1)n_(2)` is the refractive index of the second medium with respect to the first medium and the above equation represent the Snell.s law of refraction of light.