Year 12 / Quantum theory
One photon, one energy budget.
In the photoelectric effect, an absorbed photon transfers energy to an electron. An electron can escape only if the photon supplies at least the work function. Above threshold, the maximum electron kinetic energy is hf − W.
Increasing intensity at fixed above-threshold frequency increases the rate of emitted electrons, ideally, rather than their maximum kinetic energy. Increasing frequency raises maximum kinetic energy. The kinetic-energy–frequency graph has gradient h and horizontal intercept equal to threshold frequency.
A photon must clear the threshold
Explore the relationship
Below the work function no electrons are emitted. A plotted zero there denotes no emission, not emitted electrons at rest.
Maximum electron kinetic energy / eV
Tap or focus a plotted point to read its values.
View plotted data as a table
| Series | Photon energy / eV | Maximum electron kinetic energy / eV |
|---|---|---|
| Maximum electron kinetic energy / eV | 0 | 0 |
| Maximum electron kinetic energy / eV | 0.1 | 0 |
| Maximum electron kinetic energy / eV | 0.2 | 0 |
| Maximum electron kinetic energy / eV | 0.3 | 0 |
| Maximum electron kinetic energy / eV | 0.4 | 0 |
| Maximum electron kinetic energy / eV | 0.5 | 0 |
| Maximum electron kinetic energy / eV | 0.6 | 0 |
| Maximum electron kinetic energy / eV | 0.7 | 0 |
| Maximum electron kinetic energy / eV | 0.8 | 0 |
| Maximum electron kinetic energy / eV | 0.9 | 0 |
| Maximum electron kinetic energy / eV | 1 | 0 |
| Maximum electron kinetic energy / eV | 1.1 | 0 |
| Maximum electron kinetic energy / eV | 1.2 | 0 |
| Maximum electron kinetic energy / eV | 1.3 | 0 |
| Maximum electron kinetic energy / eV | 1.4 | 0 |
| Maximum electron kinetic energy / eV | 1.5 | 0 |
| Maximum electron kinetic energy / eV | 1.6 | 0 |
| Maximum electron kinetic energy / eV | 1.7 | 0 |
| Maximum electron kinetic energy / eV | 1.8 | 0 |
| Maximum electron kinetic energy / eV | 1.9 | 0 |
| Maximum electron kinetic energy / eV | 2 | 0 |
| Maximum electron kinetic energy / eV | 2.1 | 0.1 |
| Maximum electron kinetic energy / eV | 2.2 | 0.2 |
| Maximum electron kinetic energy / eV | 2.3 | 0.3 |
| Maximum electron kinetic energy / eV | 2.4 | 0.4 |
| Maximum electron kinetic energy / eV | 2.5 | 0.5 |
| Maximum electron kinetic energy / eV | 2.6 | 0.6 |
| Maximum electron kinetic energy / eV | 2.7 | 0.7 |
| Maximum electron kinetic energy / eV | 2.8 | 0.8 |
| Maximum electron kinetic energy / eV | 2.9 | 0.9 |
| Maximum electron kinetic energy / eV | 3 | 1 |
| Maximum electron kinetic energy / eV | 3.1 | 1.1 |
| Maximum electron kinetic energy / eV | 3.2 | 1.2 |
| Maximum electron kinetic energy / eV | 3.3 | 1.3 |
| Maximum electron kinetic energy / eV | 3.4 | 1.4 |
| Maximum electron kinetic energy / eV | 3.5 | 1.5 |
| Maximum electron kinetic energy / eV | 3.6 | 1.6 |
| Maximum electron kinetic energy / eV | 3.7 | 1.7 |
| Maximum electron kinetic energy / eV | 3.8 | 1.8 |
| Maximum electron kinetic energy / eV | 3.9 | 1.9 |
| Maximum electron kinetic energy / eV | 4 | 2 |
| Maximum electron kinetic energy / eV | 4.1 | 2.1 |
| Maximum electron kinetic energy / eV | 4.2 | 2.2 |
| Maximum electron kinetic energy / eV | 4.3 | 2.3 |
| Maximum electron kinetic energy / eV | 4.4 | 2.4 |
| Maximum electron kinetic energy / eV | 4.5 | 2.5 |
| Maximum electron kinetic energy / eV | 4.6 | 2.6 |
| Maximum electron kinetic energy / eV | 4.7 | 2.7 |
| Maximum electron kinetic energy / eV | 4.8 | 2.8 |
| Maximum electron kinetic energy / eV | 4.9 | 2.9 |
| Maximum electron kinetic energy / eV | 5 | 3 |
| Maximum electron kinetic energy / eV | 5.1 | 3.1 |
| Maximum electron kinetic energy / eV | 5.2 | 3.2 |
| Maximum electron kinetic energy / eV | 5.3 | 3.3 |
| Maximum electron kinetic energy / eV | 5.4 | 3.4 |
| Maximum electron kinetic energy / eV | 5.5 | 3.5 |
| Maximum electron kinetic energy / eV | 5.6 | 3.6 |
| Maximum electron kinetic energy / eV | 5.7 | 3.7 |
| Maximum electron kinetic energy / eV | 5.8 | 3.8 |
| Maximum electron kinetic energy / eV | 5.9 | 3.9 |
| Maximum electron kinetic energy / eV | 6 | 4 |
Explore: Move the work-function control and observe the emission threshold.
Photons have energy 4.8 eV and the metal has work function 2.1 eV.
- Maximum kinetic energy = 4.8 − 2.1 = 2.7 eV.
- Photons below 2.1 eV would not eject electrons in this model.
Assumed knowledge
Photon energy and graph intercepts.
Learning checkpoints & source
YOUR LEARNING CHECKPOINT- Use work function, threshold frequency and maximum kinetic energy.
- Separate intensity effects from frequency effects.
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