In Young’s double slit experiment, the two slits act as coherent sources of equal amplitude a and of wavelength λ…

Q: In Young’s double slit experiment, the two slits act as coherent sources of equal amplitude a and of wavelength λ . In other experiment with the same set up, the two slits are sources of equal amplitude a and wavelength λ , but are incoherent. The ratio of intensity of light at the mid point of the screen in the first case to that in the second case is

(a) 2 : 1

(b) 1 : 2

(c) 2 : 4

(d) 4 : 3

Ans: (a)

Sol : When sources are coherent, intensity at mid point

Imax = (a+a)2 = 4 a2

When source are incoherent, no interference occurs. Intensity at mid point,

I= I1 + I2

I = a2 + a2 = 2 a2

Imax/I = (4a2 )/(2a2 ) = 2∶1

Author: Rajesh Jha

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