Photoelectric Effect

Overview of photoelectric effect & equations

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  • Photoelectric Effect
    • EM photons allow electrons to be emitted
      • Electrons are emitted as long as the light is above the threshold frequency
        • High frequency = electrons emit quickly
        • Low frequency = electrons emit more slowly
    • Ek is independent of light intesity
      • Increasing the intensity only increases the amount of photons per second on the area
        • Because electrons can only absorb one photon of light at a time
    • Work function
      • The energy required to break the bonds that hold the electron to the metal
        • If energy gained from photon > work function then electrons are emitted
        • If energy gained from photon < work function then electrons are not emitted
      • f0 = threshold frequency
        • Electrons are emitted as long as the light is above the threshold frequency
          • High frequency = electrons emit quickly
          • Low frequency = electrons emit more slowly
      • theta = work function
      • h = Planck Constant
    • Max kinetic energy
      • Energy transferred from EM radiation to electron is the energy it absorbs from one photon
        • Photon = hf
      • Ek the electron will have when it leaves the metal = hf - other energy losses
        • Minimum Ek is the work function energy
        • Therefore, max Ek = hf - theta
          • Minimum Ek is the work function energy
          • Rearrange to give photoelectric equation
            • hf = theta + max Ek
              • Ek = 1/2mv^2  is max energy a photoelectron can have
                • This can be used to write the photoelectric equation as: hf = theta + 1/2mv^2
                  • hf = theta + max Ek
                    • Ek = 1/2mv^2  is max energy a photoelectron can have
                      • This can be used to write the photoelectric equation as: hf = theta + 1/2mv^2
      • Stopping potential
        • Photoelectrons can be made to lose their energy by doing work against an applied potential difference
        • Stopping potential =  pd needed to stop the fastest electrons travelling with max Ek
          • eVs = Ek(max)
            • where eVs = charge on electron * stopping potential in V

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