Wave Optics

Two sources of light \(0.6 \mathrm{~mm}\) apart and screen is placed at a distance of \(1.2 \mathrm{~m}\) from them. A light of wavelength \(6000\,\mathop A\limits^o\) used. Then the phase difference between the two light waves interfering on the screen at a point at a distance \(3 \mathrm{~mm}\) from central bright band is