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Question 20216
JEE Physics · Hard

Electromagnetic Waves and Wave Optics: Resultant Intensity Formula MCQ

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Resultant Intensity FormulaHardQuestion 20216

Question

Two coherent waves of intensities I₁ and I₂ with phase difference φ interfere. Resultant intensity is:
  1. A
    I₁ + I₂
  2. B
    I₁ + I₂ + 2√(I₁I₂) cosφ
    Correct
  3. C
    I₁ + I₂ − 2√(I₁I₂) cosφ
  4. D
    √(I₁I₂) cosφ

Correct answer

I₁ + I₂ + 2√(I₁I₂) cosφ

Explanation

I = I₁ + I₂ + 2√(I₁I₂) cosφ. For I₁ = I₂ = I₀: I = 2I₀(1 + cosφ) = 4I₀cos²(φ/2). Maximum (φ = 0) = 4I₀; minimum (φ = π) = 0.

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