# Physics A-Level (AQA) : 2.2 Electromagnetic radiation and quantum phenomena

Term
1 / 20
What is the photoelectric effect?
Click the card to flip 👆
Terms in this set (20)
Emission of electrons from the surface of a metal when electromagnetic radiation above a certain frequency is directed at the metal The minimum frequency of the incident electromagnetic radiation for photoelectric emission of electrons to take place Light is composed of discrete wavepackets called photons, each of energy equal to hf (i.e. proportional to frequency). When light is incident on a metal surface, an electron at the surface absorbs a single photon and gains energy hf. If the frequency of light is above a certain value (threshold frequency), the photon energy would exceed the work function of the metal, the electron would gain enough energy to overcome attractive forces, so it can escape from the metal surface.
The light intensity is directly proportional to the number of photons per second incident on the metal surface. Because each photoelectron must have absorbed one photon to escape from the metal surface, the number of photoelectrons emitted per second is therefore directly proportional to the intensity of the incident light. hf = φ + EK(max)
hf - photon energy, J or eV
φ - work function, J or eV
EK(max) - maximum kinetic energy of the photoelectrons, J or eV  Ionisation is any process of changing uncharged atoms into charged ions.
When a free electron with enough kinetic energy collides with an electron within an atom, the free electron transfers energy to the electron within the atom. If the electron within the atom gains enough energy (above ionisation energy), it can leave the atom and become free. The free electron knocks an electron out of the atom so the atom becomes a positive ion. 