Quantum physics (quantum theory, quantum mechanics)

Double slit experiment -- interpretation
classical:
• two slits are coherent sources of light
• interference due to superposition of secondary
waves on screen
• intensity minima and maxima governed by optical
path differences
• light intensity I A 2 , A = total amplitude
• amplitude A at a point on the screen
A 2 = A 1 2 + A 2 2 + 2A 1 A 2 cosφ, φ = phase
difference between A 1 and A 2 at the point
• maxima for φ = 2nπ
• minima for φ = (2n+1)π
• φ depends on optical path difference δ: φ = 2πδ/
• interference only for coherent light sources;
• For two independent light sources: no interference
since not coherent (random phase differences)
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