Photons

The photoelectric effect

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Light comes in photons with $E = hf = hc/\lambda$. Use $E[\text{eV}] \approx 1240/\lambda[\text{nm}]$.
• Brightness sets the number of photons. Colour sets the energy of each one.
• The photoelectric effect needs photons above a threshold energy.

Steps

1. Knocking out electrons
2. Photon energy
3. Violet photon
4. Sodium
5. Sodium’s threshold
6. Counting photons