A source of monochromatic light of wavelength 600 nm delivers power 3.3 × 10⁻³ W. How many photons does it emit per second? (h = 6.6 × 10⁻³⁴ J·s)
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A source of monochromatic light of wavelength 600 nm delivers power 3.3 × 10⁻³ W. How many photons does it emit per second? (h = 6.6 × 10⁻³⁴ J·s)

G1 Physics · Accepted Answer

Each photon has E = hc/λ = (6.6 × 10⁻³⁴ × 3 × 10⁸)/(600 × 10⁻⁹) = 3.3 × 10⁻¹⁹ J. Photon rate N = P/E = (3.3 × 10⁻³)/(3.3 × 10⁻¹⁹) = 10¹⁶ s⁻¹. Answer: C.