The Photoelectric Effect (Edexcel A Level Physics)

• The photoelectric effect is the phenomena in which electrons are emitted from the surface of a metal upon the absorption of electromagnetic radiation
• Electrons removed from a metal in this manner are known as photoelectrons
• The photoelectric effect provides important evidence that light is quantised, or carried in discrete packets
  • This is shown by the fact each electron can absorb only a single photon
  • This means only the frequencies of light above a threshold frequency will emit a photoelectron

Photoelectrons are emitted from the surface of metal when light shines onto it

• The photoelectric effect can be observed on a gold leaf electroscope
• A plate of metal, usually zinc, is attached to a gold leaf, which initially has a negative charge, causing it to be repelled by a central negatively charged rod
  • This causes negative charge, or electrons, to build up on the zinc plate

• UV light is shone onto the metal plate, leading to the emission of photoelectrons
• This causes the extra electrons on the central rod and gold leaf to be removed, so, the gold leaf begins to fall back towards the central rod
  • This is because they become less negatively charged, and hence repel less

Typical set-up of the gold leaf electroscope experiment