Two coherent monochromatic sources of intensities I₁ = I₀ and I₂ = 4I₀ interfere on a screen. What are the maximum intensity (I_max) and minimum intensity (I_min) observed in the interference pattern?
Answer and explanation
Correct answer: C. I_max = 9 I₀, I_min = I₀
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- Step 1: The resultant intensity of two interfering waves of intensities and with phase difference is: .
- Step 2: Maximum intensity occurs when :
- Step 3: Minimum intensity occurs when :
- Step 4: Given and :
- Step 5: Compute extremes:
Answer
I_max = 9 I₀, I_min = I₀
Why not the others: 'I_max = 5 I₀, I_min = 3 I₀' adds intensities directly without interference interference cross-terms (); 'I_max = 25 I₀' incorrectly adds intensities before squaring; 'I_max = 16 I₀, I_min = 0' squares and assumes perfect cancellation (which only happens when ).
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