For what wavelength does a 100-mW laser beam deliver 1.6 × 10¹⁷ photons in one second? (c = 3.0 × 10⁸ m/s,h = 6.626 × 10^-34 J ∙ s)

Question

Quizplus · Accepted Answer

The energy of one photon is given by E = hc/λ. The total energy delivered by the laser is 100 mW = 0.1 J/s. The number of photons is 1.6 × 10^17, so the energy per photon is 0.1 J / 1.6 × 10^17 photons = 6.25 × 10^-19 J/photon. Using E = hc/λ, we solve for λ: λ = hc/E = (6.626 × 10^-34 J∙s)(3.0 × 10^8 m/s) / 6.25 × 10^-19 J = 3.18 × 10^-7 m = 318 nm, which is closest to 320 nm.

For What Wavelength Does a 100-MW Laser Beam Deliver 1