Derive the law of reflection of light on the basis of Huygens wave theory.

Explanation

Law of reflection :
(i) The incident wavefront AB, the reflected wavefront CD and the reflecting surface XY all the in the same plane.
(ii) Angle of incidence `i=/_PAN=90^(@)-/_NAB=/_BAC`
Angle of reflection `r=/_NAD=90^(@)-/_DAC=/_DCA`
In right angled triangles ABC and ADC
`/_B=/_D=90^(@)`

`BC=AD` and AC is common
`:.` The two triangles are congruent
`:./_BAC=/_DCA`
i.e., `i=r`
Thus the angle of incidence is equal to angle of reflection.