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. `2:1`
B. `1:2`
C. `3:4`
D. `4:3`

Answer

A

Explanation

When sources are coherent, intensity at mid point is
`I_("max")=(a+a)^(2)=4a^(2)`
When sources are incoherent, no interference occurs. Intensity at mid point is
`I=I_(1)+O_(2)=a^(2)+a^(2)=2a^(2)`
`therefore" "(I_("max"))/(I)=(4a^(2))/(2a^(2))=2:1`