Question

In Y.D.S experiment the two slits act as coherent sources of amplitude A and wave length λ. In an another experiment with the same set up the two slit sources of equal amplitude A and wave length λ, but are incoherent. What is the ratio of intensity of light at mid–point of screen in the first and the second case?

Answer 1

In first case the interferring sources are coherent, constructive interference takes place at mid–point O. The resultant intensity.

I₁ = 4 A²

In second the sources are incoherent no interferring is observed at mid–point O. The resultant intensity I₂ is

I₂ = 2 A²

∴ \(\frac{I_1}{I_2}=2\)