(NB: variable power supply)
When light of a frequency above the threshold frequency is shone on the cathode, photoelectrons are ejected and then attracted to the annode. Electrons are also moving along tthe wire to provide a corrent. If the powersupply isconnected such that the cathode is +vely charged, some of the electrons will be attracted back to it, and -ve current will reduce. The faster photoelectrons will reach the annode. If the voltage is then increased, a point will be reached when even the fastest electrons will not reh the annode and the current will become zero. This voltage is called the stopping potential, Vs.
This gives us a methid for working out the minimum kinetic energy of the photoelectrons:
Max KE = Electric energy
The Measurments are reported for different frequencies of light, enabling us to measure the different maximum kinetic energies
