Practice portal › Wave Optics › Interference and Young's Double Slit Experiment
Asked in GSEB Board July 2021 · Intensity and coherent sources
Idea: the energy stored in an oscillation goes as the square of its displacement amplitude, in the same way as a stretched spring stores 1/2kx².
Intensity is the energy crossing unit area per second, so it carries that same square: I ∝ A².
When two waves superpose they combine into one resultant of amplitude A_R, and it is that single amplitude which fixes the intensity at the point.
So I_R ∝ A_R² — the intensity of the resultant wave is directly proportional to the square of the resultant amplitude.
This is why a two-slit maximum, where equal amplitudes add to 2A, is four times as bright as one slit alone rather than twice.
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