The Photoelectric Effect (Edexcel International A Level Physics)

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Lindsay Gilmour

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The Photoelectric Effect

  • 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

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Lindsay Gilmour

Author: Lindsay Gilmour

Lindsay graduated with First Class Honours from the University of Greenwich and earned her Science Communication MSc at Imperial College London. Now with many years’ experience as a Head of Physics and Examiner for A Level and IGCSE Physics (and Biology!), her love of communicating, educating and Physics has brought her to Save My Exams where she hopes to help as many students as possible on their next steps.

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