waves is studied in (XI Physics . ). When two waves simultaneously pass through a particle in a medium, the resultant displacement of that particle is the vector addition of the displacements due to the individual waves. The resultant displacement will be maximum or minimum depending upon the phase difference between the two superimposing waves.
These concepts hold good for light as well. Let us consider two light waves from the two sources S and S meeting at a point P as shown in Figure . . P S S P S P S Figure .
Superposition principle The wave from S at an instant t at P is, y = a sin ωt ( . ) The wave form S at an instant t at P is, y = a sin ( ωt + ϕ ) ( . ) . The refractive index of water, n = .
The wavelength of light in water, λ The speed of light in water, v (a) The equation relating the wavelength and refractive index is, = n Rewriting, l Substituting the values, l o o l o (b) The equation relating the speed and refractive index is, = n Rewriting, v Substituting the values, v × × v ms (c) Frequency of light in vacuum is, c = l Substituting the values, v Hz Frequency of light in water is, v = l Substituting the values, v ms Hz The results show that the frequency remains same in all media. - - - - Unit wave optics In equation ( . ) if the phase difference, ϕ = ± π , ± π , ± π . .
. , it corresponds to the condition for minimum intensity of light called destructive interference