For two equal-amplitude coherent sources, the maximum and minimum intensities are:
AI_max = I₁ + I₂; I_min = I₁ − I₂
BI_max = 4 I₀, I_min = 0 (perfect contrast)
CI_max = 2 I₀, I_min = I₀
DI_max = I_min = 2 I₀
Answer & Solution
Correct answer: B. I_max = 4 I₀, I_min = 0 (perfect contrast)
Equal-amplitude coherent sources (I₁ = I₂ = I₀): **I_max = 4 I₀** (constructive), **I_min = 0** (destructive). For unequal amplitudes: I_max = (√I₁ + √I₂)², I_min = (√I₁ − √I₂)². **Contrast ratio** = (I_max − I_min)/(I_max + I_min) = 1 only when I₁ = I₂.
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