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The interference taking place at points of maximum intensity is called constructive interference.
The interference taking place at points of minimum intensity is destructive interference.
Fringe Width
The distance between the centres of two consecutive bright or dark fringes is called the fringe width.
The angular fringe width is given by θ = λ / d. where λ is the wavelength of light d is the distance between two coherent sources.
Conditions for Constructive and Destructive Interference For Constructive Interference
Phase difference, φ = 2nπ Path difference, Δx = nλ where, n = 0, 1, 2, 3,…
For Destructive Interference
Phase difference, φ =( 2n – 1) π Path difference, Δx =( 2n – 1) π / 2 where, n = 1, 2, 3, …
If two waves of exactly same frequency and of amplitude a and b interfere, then amplitude of resultant wave is given by
R = √a 2 + b 2 + 2ab cos φ where φ is the phase difference between two waves. R max =( a + b) R min =( a – b)