3.2.2.4 Wave-particle duality

• What does electron diffraction suggest?

  Particles possess wave properties and the photoelectric effect suggest that EM waves have a particular nature
• Define diffraction

  When waves spread around an obstacle or through a gap and is defining wave property
• When is diffraction the greatest?


  When the gap the waves are passing through is similar to the wavelength
• Conclude the diffraction rings experiment?

  A beam of electrons is fired from an electron gun
• Could you explain the diffraction beam experiment?


  Electrons pass through a thin graphite screen where the carbon atoms are arranged in a lattice, acting as a diffraction grating. Electrons diffract and interfere once passed through the lattice
• Where does the screen glow?


  When the electrons strike it
• When had less diffraction occured?

  When the rings are closer together, and electrons have deivated less from their original path
• Evidence for waves as EM?

  Diffraction, interference, refractions
• Evidence for electrons as waves?

  They can diffract and interfere
• Evidence for EM waves as particles?

  Photoelectric effect
• Evidence for electrons as particles ?

  Deflect in a magnetic electric field
• The smaller the wavelength?

  Smaller the momemtum
• Longer the momentum?

  More light spreads out, smaller wavelength
• What is stopping potential?

  Minimum potential difference needed to give the metal plate a sufficient positive charge that it can attract the fastest photoelectrons back
• Light intensity is directly proportional to?

  Number of photons per second incident on the metal surface
• What happens when a free electron with enough KE collides with an electron within an atom?

  The free electron transfers energy to the electron within the atom
• When can an electron leave an atom and be free?

  If it gains enough energy (above the ionisation energy)
• The greater the de Broglie wavelength?

  Greater amount of diffraction
• What is a line spectrum?

  Spectrum of discrete lines of different colours
• Why are the lines of a line spectrum of an element characteristic of that element?

  Atoms of a certain element have unique energy levels with characteristic energy values, so photons that they emit also have characteristic energy values and wavelengths, and their line spectra are characteristic to that element
• What is the energy of the emitted photon when an atom de-excite?

  hf = E1 - E2
• What is an electron volt?

  Energy gained by an electron when moving through a potential difference of one volt