The Stopping Potential
When ligh is shone on a metal plate, photons are emitted – this is called the photoelectric effect. If the plate from which the electrons are emitted is at a potential difference relative to another plate, they will be accelerated if the second plate is at a positive potential relative to the first, and retarded if the second plate is at a negative potential relative to the first. We are especially interested in the situation where the second plate is negative relative to the first. The experimental setup is illustrated below.