The photoelectric effect

Shine light of any colour on four metals and catch the electrons.

Interactive

photon energy hf3.1eV

work function φ2.28eV

max electron KE0.82eV

stopping voltage0.82V

Wavelength λ400 nmBrightness50 %

Metal

The math, with your numbers

E = \frac{hc}{\lambda} = \frac{1240\ \text{eV·nm}}{400\ \text{nm}} = 3.1\ \text{eV}

KE_{\max} = E - \varphi = 3.1 - 2.28 = 0.82\ \text{eV}

1 eV (electronvolt) = 1.60 × 10⁻¹⁹ J, the energy an electron gains crossing 1 volt.

Try this

→Pick zinc and turn the brightness right up with red light. Any electrons? Now switch to ultraviolet at low brightness.
→Find the longest wavelength that still frees electrons from sodium. Check it with λ = 1240/φ.
→On the graph, every metal gives a line with the same slope. What is that slope?

Want to know why it behaves like this?

The lesson “Photons & Energy Levels” explains it step by step: Why can a dim blue light do what a bright red one can't?

The photoelectric effect

Shine light of any colour on four metals and catch the electrons.

The photoelectric effect

Interactive

photon energy hf3.1eV

work function φ2.28eV

max electron KE0.82eV

stopping voltage0.82V

Wavelength λ400 nmBrightness50 %

Metal

The math, with your numbers

E = \frac{hc}{\lambda} = \frac{1240\ \text{eV·nm}}{400\ \text{nm}} = 3.1\ \text{eV}

KE_{\max} = E - \varphi = 3.1 - 2.28 = 0.82\ \text{eV}

1 eV (electronvolt) = 1.60 × 10⁻¹⁹ J, the energy an electron gains crossing 1 volt.

Try this

→Pick zinc and turn the brightness right up with red light. Any electrons? Now switch to ultraviolet at low brightness.
→Find the longest wavelength that still frees electrons from sodium. Check it with λ = 1240/φ.
→On the graph, every metal gives a line with the same slope. What is that slope?

Want to know why it behaves like this?

The lesson “Photons & Energy Levels” explains it step by step: Why can a dim blue light do what a bright red one can't?