In Young’s double slit experiment, the two slits act as coherent sources of equal amplitude a and of wave length . In other experiment with the same set up, the two slits are sources of equal amplitude a and wavelength ‘’ but are incoherent. The ratio of intensity of light at the midpoint of the screen in the first case to that in the second case is
Given
Amplitude
Wave length
When sources are coherent, intensity at mid-point
When sources are incoherent, no interference occurs.
Intensity at mid point,
Therefore, the correct answer is (A).