Question is given below ? -
In Young's double slit experiment, the two slits act as coherent sources of equal amplitude a and of wavelength λ. In another experiment with the same setup, the two slits are sources of equal amplitude a and wavelength λ 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 :
(1) 2 : 1
(2) 1 : 2
(3) 3 : 4
(4) 4 : 3
In Young's double slit experiment, the two slits act as coherent sources of equal amplitude a and of wavelength λ. In another experiment with the same setup, the two slits are sources of equal amplitude a and wavelength λ 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 :
(1) 2 : 1
(2) 1 : 2
(3) 3 : 4
(4) 4 : 3
1 Answer
Explanation:
1. When two slits acts as coherent sources
Intensity is given as
#I = 4I_0cos^2(phi/2)#
At midpoint of screen intensity is maximum (
#I = 4 I_0#
2. When two slits acts as incoherent sources
If two sources are incoherent then the phase difference would arbitrarily change with time.
Average intensity is
#<< I >> = 4I_0<< cos^2(phi/2) >>#
#<< I >> = 4I_0 × 1/2 = 2I_0#
Hence, we can say that when two incoherent light sources interfere at a point, then we observe no interference pattern and intensity at all points is same and is equal to
So, ratio will be
#4I_0 : 2I_0 = "2 : 1"#
