Two monochromatic sources A and B emit the same number of photons per second. Let the wavelength of source A be λ₁ = 400 nm and that of source B be λ₂ = 600 nm. The power radiated by source B is:
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Question

Two monochromatic sources A and B emit the same number of photons per second. Let the wavelength of source A be λ₁ = 400 nm and that of source B be λ₂ = 600 nm. The power radiated by source B is:

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G1 Physics · Accepted Answer

Step 1: Each source emits the same number N of photons per second, so power P = N(hc/λ). Step 2: Therefore P ∝ 1/λ. Since λ₂ = 600 nm > λ₁ = 400 nm, P₂/P₁ = λ₁/λ₂ = 2/3. Hence source B radiates less power. Correct answer: B.