Question

What is the wavelength of light (in nm) if 1.21x10^21 photons have a total energy of 432 J?

Answer 1

The wavelength is 556 nm.

Energy per photon = 432 J/1.21 × 10²¹ photons = 3.570 × 10⁻¹⁹ J/photon

fλ = c, so f = c/λ

E = hf = (hc)/λ

λ = (hc)/E = (6.626 × 10⁻³⁴ J·s × 2.998 × 10⁸ m·s⁻¹)/3.570 × 10⁻¹⁹ J = 5.56 × 10⁻⁷m =  556 nm