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A2/A-level Physics - The Photoelectric Effect

OCR Physics A Unit 2, the Photoelectric Effect,

· A2 Physics,a-level physics,Photoelectric effect,OCR Physics A unit 2,Threshold frequency

The Photoelectric Effect

If you shine light of a high enough frequency onto the surface of a metal, it will emit electrons. This is the photoelectric effect.

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Experiments show that:

  1. Increasing intensity increased number of photoelectrons emitted.
  2. For a light below a certain threshold frequency, no electrons are emitted.
  3. The maximum kinetic energy of the photoelectrons increases with frequency, but is unaffected by the intensity.
The three points above are very important, you must know them for A2/A-level Physics exam! 👨‍🏫

The photoelectric effect couldn't be explained with wave theory...

  • No explanation for 2, lower frequency light should just take longer to emit electrons.
  • No explanation for 3, energy should be proportional to intensity.
  • Although diffraction & interference (unique wave properties) provided evidence for a wave nature…

The photon model explained the photoelectric effect...

  • When light hits a surface, it is bombarded by photons.
  • If one of these collides with a free electron, the electron will gain the energy hf.
  • Before an electron can leave the metal, it needs energy to break the bonds holding it there.
    • work function energy = Φ

Threshold frequency (2) explanation:

  • If there isn’t enough energy, the electrons will just vibrate a bit, and release energy as another photon, causing the metal to heat up but not emit electrons.
  • f = Φ ÷ h
  • f = threshold frequency
  • the minimum frequency of radiation that will produce a photoelectric effect.

Maximum Kinetic energy (3) explanation:

  • KE independent of intensity as electrons can only absorb one photon at a time.
  • hf = Φ + ½mv2
  • hf = energy delivered by photon

Photoelectric Effect

  • Energy is conserved when a photon interacts with an electron.
  • Photoelectric current in a photocell is proportional to intensity of the incident radiation, as a higher intensity means more photons and thus more electrons released, leading to a greater current.

Reference:

https://getrevising.co.uk/resources/quantum_physics

This is the end of the topic!

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Drafted by Cherry (Chemistry)

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