Physics
Photoelectric effect and light quanta
Photoelectric effect
Photoelectric effect: the emission of electrons from a substance under the action of light.
Einstein's equation:
hν = A_ch + E_k,max
Here h = 6,63·10⁻³⁴ J·s (Planck's constant), A_ch is the work function.
Threshold frequency
- Threshold (red limit) frequency: ν_min = A_ch/h.
- If the frequency is less than ν_min, no photoelectric effect occurs.
- This does not depend on intensity: no matter how strong the light is, no electrons are emitted at a low frequency.
Photon
| Quantity | Formula |
|---|---|
| Photon energy | E = hν = hc/λ |
| Photon momentum | p = h/λ |
Light is a stream of quanta (photons).
History
- The photoelectric effect was observed by Hertz (1887).
- Its laws were studied by A. G. Stoletov.
- It was explained by Einstein (1905), for which he received the 1921 Nobel Prize.
Calculation method: the energy of the emitted electron is E_k = hν − A_ch. The units must be the same: both sides in joules or both in electronvolts.
- Find the photon energy: hν
- Subtract the work function: A_ch
- What remains is E_k,max