August 12, 2021
The Photoelectric Effect
If you shine light of a high enough frequency onto the surface of a metal, it will emit electrons. This is the photoelectric effect.
Experiments show that:
- Increasing intensity increased number of photoelectrons emitted.
- For a light below a certain threshold frequency, no electrons are emitted.
- The maximum kinetic energy of the photoelectrons increases with frequency, but is unaffected by the intensity.
The three points above are very important, you must know them for A2/A-level Physics exam! 👨🏫
The photoelectric effect couldn't be explained with wave theory...
- No explanation for 2, lower frequency light should just take longer to emit electrons.
- No explanation for 3, energy should be proportional to intensity.
- Although diffraction & interference (unique wave properties) provided evidence for a wave nature…
The photon model explained the photoelectric effect...
- When light hits a surface, it is bombarded by photons.
- If one of these collides with a free electron, the electron will gain the energy hf.
- Before an electron can leave the metal, it needs energy to break the bonds holding it there.
- work function energy = Φ
Threshold frequency (2) explanation:
- If there isn’t enough energy, the electrons will just vibrate a bit, and release energy as another photon, causing the metal to heat up but not emit electrons.
- f = Φ ÷ h
- f = threshold frequency
- the minimum frequency of radiation that will produce a photoelectric effect.
Maximum Kinetic energy (3) explanation:
- KE independent of intensity as electrons can only absorb one photon at a time.
- hf = Φ + ½mv2
- hf = energy delivered by photon
Photoelectric Effect
- Energy is conserved when a photon interacts with an electron.
- Photoelectric current in a photocell is proportional to intensity of the incident radiation, as a higher intensity means more photons and thus more electrons released, leading to a greater current.
Reference:
https://getrevising.co.uk/resources/quantum_physics
This is the end of the topic!
Drafted by Cherry (Chemistry)