• Energy Levels & Photon Emission Flashcards
What is a vacuum photocell?
Glass tube that contains a metal plate ( referred to as the photocathode ), and a smaller metal electrode referred to as the anode.
What is the photocathode?
Metal plate
What is the anode?
Small metal electrode
How does a vacuum photocell work?
- When light of a frequency greater than the threshold frequency for the metal is directed at the photo-cathode electrons are emitted from the cathode and are attracted to the anode
- Micromameter in the circuit can be used to measure the photoelectric current.
- This is proportional to the number of electrons per second that transfer from the cathode to the anode.
What is the path of electrons in a vacuum photocell?
Emitted from the cathode, and attracted to the anode.
What is the formula for the number of photo-electrons per second that are transferred?
• Number of photo-electrons per second transferred from the cathode to the anode.
• I/e
e = charge of electron
i = photoelectric current
What is the photoelectric current proportional to?
• The photoelectric current is proportional to the intensity of the light incident on the cathode.
What is the light intensity?
- The light intensity is a measure of the energy per second carried by the incident light.
- Proportional to the number of of photons per second incident on the cathode.
Why is number of photons per second incident proportional to light intensity?
- Each electron has absorbed one photon to escape from the metal surface.
- Number of photo electrons emitted per per second, is therefore proportional to the intensity of the incident light.
What does light intensity not affect?
- Intensity of incident light does not affect the maximum kinetic energy of a photo electron.
- Regardless of the intensity of light, energy gained by a photo electron is due to the absorption of one photon only.
What is the formula for the maximum kinetic energy of a photo electron?
Ekmax = hf - Φ
