A pulsed laser has an average output power of 4.0 W. Each pulse consists of light at wavelength 5.0 × 10^-⁷ m and has a 25 ms duration. How many photons are emitted in a single pulse? A)1.0 × 10¹⁷ B)2.5 × 10¹⁷ C)3.7 × 10¹⁷ D)5.0 × 10¹⁷ E)7.4 × 10¹⁷

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Quizplus · Accepted Answer

The energy of a single pulse is given by the power multiplied by the duration: $ E = 4.0 \, \text{W} \times 0.025 \, \text{s} = 0.1 \, \text{J} $. The energy of a single photon is $ E_{\text{photon}} = \frac{hc}{\lambda} $, where $ h = 6.63 \times 10^{-34} \, \text{Js} $ and $ c = 3.0 \times 10^8 \, \text{m/s} $. Substituting the values, $ E_{\text{photon}} = \frac{6.63 \times 10^{-34} \times 3.0 \times 10^8}{5.0 \times 10^{-7}} = 3.978 \times 10^{-19} \, \text{J} $. The number of photons is $ \frac{0.1}{3.978 \times 10^{-19}} \approx 2.5 \times 10^{17} $.

A Pulsed Laser Has an Average Output Power of 4