The Photoelectric Effect

In a Photocell, a photon is coming in with Energy

E_photon = hf = pc

If the photon has enough energy, it will “kick out” or emit electrons from atoms in metal cathode.

The Photocell is then connected to a circuit, and the freed electrons travel in the circuit and create a photocurrent.

We can find the kinetic energy of these electrons by supplying a very small voltage difference between the anode and cathode, opposing the photocurrent. The smallest voltage that stops the photocurrent is V_s.

 

• The current arises from photoelectrons emitted from the negative plate and collected at the positive plate;

• For each metal, there is a threshold frequency below which no electrons are emitted;

• The number of electrons emitted is proportional to intensity of radiation;

• Emitted electrons have KE up to a maximum value, which depends on the frequency of radiation (unexplained by classical physics).

• When the applied potential difference is equal to or more negative than -ΔVs, the stopping potential, no electrons reach the anode, and the current is zero.

• The stopping potential is independent of the radiation intensity.

• Some electrons are ejected with slower speeds. The most energetic electrons have KE_MAX = e∆V_S