Photoelectric Effect Flashcards
What’s the photoelectric effect?
When light with enough frequency is shone on a metal’s surface, electrons are emitted. For most metals frequency is in the UV range.
It proves light is quantised.
Summarise the physics behind the photoelectric effect…
- Free electrons on the surface absorb light energy and so vibrate.
- If an electron absorbs enough energy, bonds break and photoelectrons are released.
What are three conclusions of the photo-electric effect?
- No photoelectrons are emitted below the threshold frequency.
- Photoelectrons are emitted with kinetic energies from zero to the maximum, which increases with frequency and isn’t affected by intensity.
- Number of photoelectrons emitted per second is proportional to radiation intensity.
How would the photo-electric effect work according to wave theory?
For a particular frequency of light, energy is proportional to intensity, and would be spread evenly on the wavefront. Each free electron on the metal would gain a bit of energy with each wave, with electrons gradually gaining enough energy to leave the metal.
What problems are there with the wave theory discussion?
A lower frequency would increase time for electrons to gain energy. There is no explanation for the threshold frequency.
The higher the intensity of the wave, the more energy It should transfer to each electron. KE should rise with intensity, but KE relies solely on frequency.
Describe the photoelectric effect with the photon model…
When light hits a surface, the metal is bombarded by photos. If a free electron absorbs one, it will gain energy equal to hf, so a higher frequency means more kinetic energy. Only one photon is absorbed at a time, so it needs to supply all the energy, enough for release. More photons with increased intensity won’t affect kinetic energy.
What’s the work function?
If the work function isn’t exceeded, the metal will only heat up. hf>o, so f=o/h.
