Relation between phase difference and path difference is \\\\(\\phi = \\dfrac{2\\pi}{\\lambda} \\delta\\\\)where \\\\(\\lambda\\\\) is the wavelength of the wave.For constructive interference : Path difference \\\\(\\delta = n\\lambda\\\\) \\\\(\\implies \\ \\phi = 2n\\pi\\\\)where \\\\(n = 0, \\ 1,\\ 2, \\ ...\\\\)For destructive interference : Path difference \\\\(\\delta = (n+\\dfrac{1}{2})\\lambda\\\\) \\\\(\\implies \\ \\phi = (2n+1)\\pi\\\\)