Question

In Young's double-slit experiment, the two slits act as coherent sources of equal amplitude $A$ and of wavelength $\lambda$. In another experiment with the same setup, the two slits are sources of equal amplitude $A$ and wavelength $\lambda$, but are incoherent. The ratio of intensity of light at the mid-point of the screen in the first case to that in the second case is

• A. $1:1$
• B. $1:2$
• C. $2:1$
• D. $4:1$

Answer 1

The correct option is C $2:1$

in first case the intensity is $(\sqrt{I}+\sqrt{I}{)}^2=4I$
in second case intensity is $I+I=2I$
ratio is $2:1$
option $C$ is correct