In Young's double slit experiment, the two slits act as coherent sources of equal amplitude A and 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 average intensity of light at the midpoint of the screen in the first case to that in the second case is:-
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Question

In Young's double slit experiment, the two slits act as coherent sources of equal amplitude A and 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 average intensity of light at the midpoint of the screen in the first case to that in the second case is:-

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G1 Physics · Accepted Answer

For coherent equal-amplitude waves at the midpoint, amplitudes add and the intensity is 4A². For incoherent waves, intensities add and the average intensity is 2A². Therefore the ratio is 4A²:2A²=2:1. Option B.