In the arrangement shown in the figure, S1 and S2 are two parallel slits at a separation d. There is a screen at a distance` D (gtgtd)` from the slits. Two point sources A1 and A2 have been placed symmetrically with respect to the slits at a large distance with`ltltA_(1)OO_(1)=ltltA_(2)OO_(1)=Deltatheta`. The sources are monochromatic giving out light of wavelength l but they are incoherent. Write the intensity of light at a point P on the screen as a function of y. Take`I_(0)` to be maximum intensity on the screen when one of the two sources (A1 and A2) is switched on. Assume y to be small.

Answer

`I_(0)cos^(2)[(2pi)/(lambda)d((yd)/(D)+sinDeltatheta)]+I_(0)cos^(2)[(2pi)/(lambda)d((yd)/(D)-sinDeltatheta)]`