• 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