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

Options

A. `1:2`
B. `2:1`
C. `4:1`
D. `1:1`

Answer

B

Explanation

`I_(1)=I_(2)=I^(')`, at midpoint of screen, `Deltax=0, phi=0`
For coherent sources, `I_(R)=(sqrt(I_(1))+sqrt(I_(2)))^(2)=4I^(')`
For incoherent source, `I_(R)^(')=I_(1)+I_(2)=2I^(')`
`I_(R)/I_(R)^(')=(4I^('))/(2I^('))=2/1`