Two point sources S 1 and S 2 separated by a distance 10 μ m emit light waves of wavelength 4 μ m in phase. A circular wire of radius 40 μ m is placed around the sources as shown in figure, then ( O is the centre of the circle and O S 1 = O S 2 )

Step-by-step solution

In cases of B   &   D the path, the difference is zero so phase difference is also zero gives bright image while in case of A   &   C path difference is, 10   μm ⇒ ∆ p = 10   μm and we can calculate there are 10 4 λ = 5 2 λ , which gives dark fringe.