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

Options

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

Answer

c

Explanation

In the second case,
`I = I_(0) + I_(0) + 2 I_(0) cos 0^(@)`
or `I = 4 I_(0)`
In the second case
`I' = I_(0) + I_(0) = 2 I_(0)`
`:. (I)/(I') = (4 I_(0))/(2 I_(0)) = (2)/(1)`