Quark Phenomena

• Why does the kinetic energy of emitted electrons have maximum values?

  hf is the energy received from photons

  • Photons have energy dependent on frequency
  • A one-to-one interaction between photon and electron
  • Max KE = hf - work function
  • More energy required to remove deeper electrons; amount of energy required to remove electrons varies.
  • Therefore, KE of electrons will vary.
• Why will electrons not be emitted if the frequency of radiation is below a certain value?

  Work function is the minimum amount of energy required to release an electron

  The energy of a photon is directly proportional to the frequency of radiation

  • So lower frequency means not enough energy is able to be transferred and release the electron.
• How to suggest something possesses wave properties

  Diffract or Interfere
• Photoelectric effect

  • Photons of light incident on the metal surface cause the emission of electrons
  • Electrons emitted are those near the metal’s surface.
• Electron-volt (eV)

  Work done to accelerate an electron through a potential difference of 1V.

  • 1 eV is equal to the charge of an electron (E = qv)
• Stopping Potential

  The minimum potential difference required to stop the highest kinetic energy electrons from leaving the metal plate in the photoelectric effect
• Work Function

  The minimum energy required to remove an electron from a metal’s surface
• Threshold Frequency

  The minimum frequency of photons require for photoelectrons to be emitted from the surface of a metal plate through the photoelectric effect
• Photon

  A discrete packet of energy
• Why does a photon behave like a particle?

  • Is a packet of electromagnetic energy; gives the idea of an ‘item’
  • Travels in one direction only; light emits particles in all possible directions, each individual photon travels in one direction only.
  • Energy of a single photon is ‘quantified’ and measurable
• The electromagnetic spectrum is a continuous spectrum of all the possible frequencies of electromagnetic radiation.
• E2 - E1 = hf
• Two ways to excite an electron

  1. Collision with another electron with energy equal to or greater than the energy between two energy levels
  2. Absorption of a photon with exactly the same amount of energy as the energy between two energy levels
• Ground state

  Electrons on the lowest energy level (innermost orbs) are in the ground state

  • Have the lowest potential energy.
• Explain why energy levels are negative

  An electron outside the atom is defined to have zero (potential) energy.

  • Ground state of electrons have the lowest energy
  • Electrons outside the atom have zero energy
  • So energy has to be provided for a electron to go to zero; therefore must be negative.
• All elements have their own line spectrum when any electric charge is passed through their vapour.
• Lines on the spectrum are the wavelengths of the light produced by the discharge through a gas.
• Electrons are emitted by the cathode in the tube and accelerated by the potential difference between the ends

  • Collides with the atoms
  • Excites electrons which then drop back down emitting light (wavelength)
• Light intensity affects the number of electrons emitted per second.

  • Does not impact the frequency.
• Ionisation

  Any process of creating ions.

  • Giving electrons enough energy to leave the atom.
• Excitation

  Atoms absorbing energy and their electrons moving up energy levels without being ionised.

  • Occurs at certain energies; characteristic of the gas.
• Ground state

  The lowest energy state of an atom.
• Wavelengths of lines of a line spectrum are characteristic of the atoms of that element.

  Energy levels of each type of atom are unique to that atom.

  • Photons emitted are characteristic of the atom.
• Electron diffraction suggests particles possess wave properties
• Photoelectric effect shows electromagnetic waves having a particulate nature.