Quantum

Quantum means discrete quantity

Quantum physics relies on discrete energy; a specific, defined amount of energy, which if changed breaks things

Wave particle duality

Particles behaving like a wave at the same time

Wave characteristics

  • Reflection
  • Refraction
  • Diffraction
  • Interference
  • Doppler effect
  • Young’s double – slit experiment used to show something is a wave
  • Electron diffraction tube experiement shows electrons can be waves

Particles

  • Have mass
  • Produce momentum & force
  • Fundamental particle
  • Reflect
  • Refract
  • Do not diffract
  • Does not interfere
  • Photoelectric effect shows light can be a particle

Photoelectric effect

A photon provides a single electron with enough energy to emit a photoelectron from the surface of a metal. The amplitude makes no difference to the ratio, as would be expected by a wave. The energy of the electron is dependent on the frequency of the photon. There is no time interval between the photon hitting the metal, & the electron being released, a property of a particle

Work function - $\phi$
Minimum amount of energy a photon requires to discharge an electron from the surface of a metal
Threshold frequency
Minimum frequency required for work function. Important as it’s the minimum frequency required for emission to take place
Stopping potential
Energy required per unit charge to make kinetic energy 0

Equations

\begin{align}E=\phi\ +E_{k\ max}\end{align}

\begin{align}E=hf_{\phi}+\frac{mv^2}{2}\end{align}

Where $\phi$ is the threshold frequency of the metal, and $E_{k\ max}$ is the maximum kinetic energy of an exiting electron

Electron diffraction tube experiment

Charged electrons pass through gaps between carbon atoms in a disc, & diffract, forming rings on the screen.

Incandescence

  • When the temperature of an object is high enough, it is possible for light to be emitted as well as thermal radiation

Spectra

Continuous spectrum
Spectrum with no missing wavelengths
Absorbtion spectrum
Spectrum with some missing wavelengths
Some wavelengths will be absorbed enroute to the detector
Emission spectrum
Spectrum with only a few discrete wavelengths present

Electron energy absorbtion and emission

Electrons in an atom or ion can absorb energy, which causes them to move from the ground state to a higher energy level, which results in absorbtion spectrums. After a short time, the electron will return to ground state, and emmit one or more photons of specific, discrete wavelengths, which can be shown on a emission spectrum

Lyman series
Emmitted photon in the UV range
Balmer series
Emmitted photon in the visible light range
Paschen series
Emmitted photon in the IR range

How do fluorescent tubes work?

In a sealed glass tube, containing mercury & argon, under low pressure. The tube has electrodes emitting electrons from thermionic emission, absorbed by the mercury, which releases UV which are absorbed by a fluorescent phosphor coating, which release visible light