A laser emits a pulse of light that lasts 10 ns. The light has a wavelength of 690 nm, and each pulse has an energy of 480 mJ. How many photons are emitted in each pulse? (c = 3.0 × 10⁸ m/s, h = 6.626 × 10^-34 J ∙ s) A) 1.7 × 10¹⁸ B) 2.1 × $10^{27}$ C) 2.6 × $10^{37}$ D) 3.1 × $10^{43}$

Question

Quizplus · Accepted Answer

The energy of a single photon is given by E = hc/λ. Substituting the given values, E = (6.626 × 10^-34 J∙s)(3.0 × 10^8 m/s) / (690 × 10^-9 m) = 2.88 × 10^-19 J. The number of photons is the total energy divided by the energy per photon: 480 mJ / 2.88 × 10^-19 J = 1.7 × 10^18 photons.

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A Laser Emits a Pulse of Light That Lasts 10 $10^{27}$