Radiation

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    • What is the electronvolt?
      The energy gained by an electron accelerated through a potential difference of 1 V
    • 1 eV = 1.6 x 10 ^ -19 J
    • How do you convert from eV to J?
      Multiply by 1.6 x 10^-19
    • How do you convert from J to eV?
      Divide by 1.6 x 10^-19
    • What is the photoelectric effect?
      The emission of electrons from a metal surface when electromagnetic radiation is incident
    • Why must the light be incident on a METAL for the photoelectric effect to occur?
      The phenomenon is to do with delocalised electrons
    • What are electrons that are removed from a metal via the photoelectric effect referred to as?
      Photoelectrons
    • What does the photoelectric effect prove?
      The particle nature of light
    • Define threshold frequency.
      The minimum frequency of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal
    • How does threshold frequency prove the particle nature of light?
      If light was a wave, any frequency would cause photoelectric emission as the energy absorbed by each electron would gradually increase with each incoming wave. The emission would instead depend on amplitude.
    • Define the work function of a metal.
      The minimum energy required to release a photoelectron from the surface of a metal
    • Why is a photoelectron only emitted for radiation above the threshold frequency?
      Each electron can absorb one photon. It is a one on one interaction.
    • The work function is a property of the metal
    • Define stopping potential
      The potential difference required to stop photoelectron emission from occurring and reduce the current to 0
    • Why is stopping potential important?
      Allows us to find maximum kinetic energy of the released photoelectrons
    • Ek(max) = e x Vs
      • Ek(max) = maximum kinetic energy
      • e = charge of an electron
      • Vs = stopping potential
    • What is the photoelectric equation?
      hf = ϕ + Ek(max)
      • h = Planks constant
      • f = frequency
      • ϕ = work function
      • Ek(max) = maximum kinetic energu
    • Photoelectric equation
      Energy of an incident photon = work function + maximum kinetic energy of the photoelectron
    • What effect does increasing brightness have on the maximum kinetic energy of photoelectrons?
      No effect
    • What effect does increasing brightness have on the photocurrent?
      It increases
    • What effect does increasing frequency have on the maximum kinetic energy of photoelectrons?
      Increases
    • What effect does increasing frequency have on the photocurrent?
      No effect
    • What does the intensity of light mean?
      The number of photons arriving per second
    • Graph for the PE equation
      A) h
      B) threshold frequency
      C) work function
    • The kinetic energy of the photoelectrons is independent of the intensity of light because each electron can only absorb one photon
    • What is the kinetic energy of photoelectrons dependent on?
      Frequency
    • What is the kinetic energy of photoelectrons independent of?
      Intensity
    • What affect will increasing the intensity of light have?
      It will increase the number of photoelectrons emitted
    • Why is the kinetic energy a maximum?
      Work function is the minimum energy. Most electrons are lower down and therefore require more energy to escape the surface
    • What is the photoelectric current?
      The number of photoelectrons emitted per second
    • What is photoelectric current proportional to?
      The intensity of the incident radiation
    • To sum up:
      • Intensity = more photons
      • Frequency = more energy
    • What is ionisation?
      The removal, or addition, of an electron from, or to, an atom when given sufficient energy
    • What is the excitation of electrons?
      When an electron is given enough energy to move up an energy level, but not enough to leave the atom
    • Two ways of excitation:
      1. Absorb photon
      2. Collide with free electron
    • In ionisation, the electron is completely removed from the atom
    • How are electrons excited?
      Absorption of energy equal to the difference between energy levels
    • In ionisation, the photon can transfer any quantity of energy above the ionisation energy
    • When an electron de-excites, it releases the energy it gained in the form of a photon
    • What are fluorescent tubes filled with?
      Mercury vapour
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