The wave length of light ? = 650nm
the seperation between slits d = 4.50?m
the distance between screen D = 4.0m
the postion of point P is y = 13cm
(a) The position of P in terms of phase difference
          ? =
2?/? dsin?
            Â
=[ 2?/(650*10^-9)](4.5*10^-6)(y/D)
since for small angles sin? ? tan? = y/D
          Â
= 0.0435*10^3 (13*10^-2/4)
          Â
= 0.45? rad = 1.413 rad
(b) The ratio of intensity
         Â
I/I0 = 4cos^2(?/2)
                Â
= 4cos^2(1.413/2)
                 Â
=2.3
