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)

Question

Quizplus · Accepted Answer

The number of photons in each pulse can be calculated using the energy of a single photon and the total energy of the pulse. The energy of a single photon is given by $E = \frac{hc}{\lambda}$, where $h$ is Planck's constant, $c$ is the speed of light, and $\lambda$ is the wavelength of the light. Substituting the given values, $h = 6.626 \times 10^{-34} \, \text{J} \cdot \text{s}$, $c = 3.0 \times 10^8 \, \text{m/s}$, and $\lambda = 690 \times 10^{-9} \, \text{m}$, we find the energy of a single photon. The total number of photons is then the total pulse energy divided by the energy of a single photon, $N = \frac{480 \times 10^{-3}}{E}$. Calculating with the given values leads to the correct order of magnitude as in option A.

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