wave particle duality

• newtons corpuscular theory explained reflection as particles colliding with a surface, a repulsive force pushing them back and so a change in perpendicular velocity
• newtons corpuscular theory explained refraction as particles approaching a surface, a short range force of attraction increasing their perpendicular velocity and so they move towards the normal
• newtons corpuscular theory claimed that light travels faster in denser mediums
• Huygens wave theory claimed that light travels slower in denser mediums
• newtons corpuscular theory can not explain diffraction
• Huygens wave theory can explain diffraction
• if corpuscular theory was right, youngs double slit would produce 2 bright fringes in line with slits
• Youngs double slit demonstrated diffraction and interference (properties of wave theory) but Huygen was still not accepted due to newtons reputation
• calculation of speed of light disproved newtons corpuscular theory
• $\mu o$is the permeability of free space which is the magnetic flux density due to a current carrying wire
• $\epsilon o$ is the permittivity of free space which is the electric field strength due to a charged object in free space
• the speed of radio waves in hertz experiment agreed with Maxwell and

  showed radio waves were EM waves
• in hertz experiment, the detection of waves when receiver was perpendicular was a maximum and when it was parallel it was a minimum. this shows radio waves are polarised
• the speed of light calculated in fizeaus experiment agreed with maxwells formula which showed visible light is an EM wave
• a black body is an object that absorbs and emits all possible wavelengths of radiation
• wave theory predicted that as wavelength decreases, intensity increases which predicts that an infinite amount of uv radiation will be emitted. this didn't agree with experimental evidence, leading to the ultraviolet catastrophe
• Planck suggested EM waves travel in discrete packets called quanta
• the problems with wave theory and the photoelectric effect

  • suggests that any frequency of light can cause emission
  • suggests time is needed to reach work function
  • suggests increasing intensity increases emission
  • suggests photoelectrons are released with specific kinetic energy
• there is a proportional relationship between fringe spacing in an electron diffraction pattern and de Broglie wavelength
• increasing the speed of electrons in electron diffractions means the rings are closer together
• resolving power is the ability to distinguish between close structures
• wavelength is inversely proportional to resolving power
• TEM stands for transmission electron microscope
• in a TEM, the electron beam passes through 3 lenses

  1. condenser lens - deflects electrons to form parallel beam
  2. objective lens - forms image of sample
  3. projector lens - magnifies image and projects onto screen
• to produce a voltage for resolving details the size of the atom, set the de Broglie wavelength to the diameter of the atom (0.1nm). put this into $\lambda=$$\frac{h}{\sqrt{2meV}}$to get V=150.8V
• STM stands for scanning tunnelling microscope
• an STM involves a fine tipped probe that moves across the surface of an object at constant potential, creating a tunnelling current that maps the surface of the material
• 2 modes for an STM

  1. constant height mode - change in tunnelling current recorded to map surface
  2. constant current mode - change in height recorded to map surface
• Quantum tunnelling shows the wave nature of particles and is when electrons have to overcome a potential barrier and they are able to do it without enough energy
• hertz experiment

  • high pd supplied over a small gap
  • spark produced in gap
  • spark also produced in loop receiver in front of it due to the wave acting as an alternating magnetic field and inducing an emf
  • determined the waves were radio waves
  • measure wave speed with frequency x wavelength
• fizeaus experiment

  • light passes through a gap in a rotating wheel
  • its travels to a distant mirror (8.6km) and reflects back
  • if the wheel is rotating very slowly, the light passes through the same gap
  • when the wheel rotates at a certain speed, the reflected light hits a tooth rather than a gap and can't be observed
  • the speed of the light can be measured with 4dNf