Question

Light from two coherent sources of the same amplitude $A$ and wavelength $\lambda$ illuminates the screen. The intensity of the central maximum is $I_0$. If the sources were incoherent, the intensity at the same point will be

• A. $4I_0$
• B. $2I_0$
• C. $I_0$
• D. $\frac{I_0}{2}$

Answer 1

Answer: (D)

$\frac{I_0}{2}$

Answer 2

The rays of light from two coherent sources superimpose each other on the screen forming alternate maxima (with maximum intensity $I_{0}$ ) and minima (with intensity zero). If two non-coherent sources superimpose, there will be no maxima and minima, instead the intensity will be $\frac{I_{0}}{2}$ throughout.