A 200 W sodium street lamp emits yellow light of wavelength 0.6 µm. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is

Question

Dr. Abubacker · Accepted Answer

[Solution from source] Light power = 25% of 200 W = 50 W. Energy per photon = hc/λ = (6.63 × 10⁻³⁴ × 3 × 10⁸)/(0.6 × 10⁻⁶) ≈ 3.3 × 10⁻¹⁹ J. Number per second = 50/3.3 × 10⁻¹⁹ ≈ 1.5 × 10²⁰. Using the full 200 W gives about 6 × 10²⁰, ignoring the efficiency. Answer (2).

Q. A 200 W sodium street lamp emits yellow light of wavelength 0.6 µm. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is

Explanation

Reviewed by Dr. Abubacker

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