In 1834,Lloyd devised a convenient method to obtain two coherent sources of light to produce sustained interference.There are two sources S1 and S2.Here S1 is the real source while S2 is the reflected virtual image of the source S1.The resultant displacement is given by
= Re
i(wt - θ)
(1)Intensity is maximum, when
(x2 - x1) = (2n ± 1) * (λ/2)
So the maximum intensity occurs when the path difference is an odd multiple of (λ/2).
(2)Intensity is minimum when
(x2 - x1) = (2n + 2) * (λ/2) or 2n(λ/2)
Thus when the path difference is an even multiple of (λ/2),the intensity becomes zero.
The wavelength is given by
λ = [(β.(2d)/D)].