A laser emits a single,3.0-ms pulse of light that has a frequency of 2.83 × 10¹¹ Hz and a total power of 65 000 W.How many photons are in the pulse?
A)6.0 × 10²³
B)1.2 × 10²⁴
C)2.4 × 10²⁵
D)3.6 × 10²⁵
E)4.8 × 10²⁶

Question

Quizplus · Accepted Answer

The number of photons in the pulse can be calculated using the formula: number of photons = (total energy of the pulse) / (energy of one photon). The total energy of the pulse is power × time = 65,000 W × 3.0 × 10^-3 s = 195 J. The energy of one photon is given by E = hf, where h is Planck's constant (6.626 × 10^-34 J·s) and f is the frequency of the light (2.83 × 10^11 Hz). Thus, E = 6.626 × 10^-34 J·s × 2.83 × 10^11 Hz = 1.875 × 10^-22 J per photon. Therefore, the number of photons = 195 J / 1.875 × 10^-22 J/photon ≈ 1.04 × 10^24, which rounds to 1.2 × 10^24, making option B the correct answer.

A Laser Emits a Single,3