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 intensities 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 of mid point is
`I_(max) = (a + a)^(2) = 4a^(2)`
Now, when sources are incoherent, no interference occurs, intensity at mid point is
`I=I_(1)+I_(2) rArr a^(2)+a^(2)=2a^(2)`
`:. (I_(max))/(I)=(4a^(2))/(2a^(2))=2:1`