Problem — Energy of a green photon at 530 nm

Problem

Green light has wavelength $\lambda = 530$ nm. Calculate the photon energy in eV using the rule of thumb $E(\text{eV}) \approx 1240/\lambda(\text{nm})$.

Solution

Step 1 — Rule of thumb. The constant $hc$ is about $1240$ eV·nm, so the energy of a photon of wavelength $\lambda$ (in nm) is

$E = \frac{hc}{\lambda} \approx \frac{1240}{\lambda(\text{nm})}\;\text{eV}$

Step 2 — Substitution.

$E = \frac{1240}{530} \approx 2{,}34\;\text{eV}$

$\ev{E \approx 2{,}34\;\text{eV}}$

A value of a few eV is typical of visible-light photons — precisely the energy scale of outer electronic transitions in atoms.

Collegamenti

Argomenti: Quantum physics Concetti: Photon Competenze: Unit conversion