Wave Particle Duality
Do you still remember wave particle duality in AS/A-Level Physics?
- The wave particle duality theory states that light behaves as a particle AND a wave at the same time.
- Light as a Wave
- Interferance patterns produced by diffraction shows that light is a wave because in order for diffraction to occur, waves are required to superimpose to form those patterns. Particles can't superimpose in this way. Polarisation also show how light can behave as a wave.
- Light as a Particle
- Max Planck suggested that light travels in quantised packets of energy called photons. Photons are massless and travel at the speed of light (3x108) The energy of the photon is proportional to the frequency and are linked by this equation:
Energy of a Photon (in J) = Planck's Constant x Frequency(Hz)
Planck's constant = 6.63x10-34 J s-1
- Photon energies are so small so they are given in electron volts (eV). An electron volt is the energy gained by an electron through a potential difference. 1eV = 1.6x10-19J
- Electron Diffraction
- Electrons fired by an electron gun pass through graphite which acts as a diffraction grating. The electrons interfere with each other and and get diffracted. This shows. how particles can have wave-like properties.
- De Broglie
- The De Broglie law shows that any particle that has momentum also has a wavelength.
De Broglie Wavelength = Planck's Constant / Momentum
Photon and Absorbtion and Emmission
Photon Absorbtion:
When a photon is absorbed by an electron the electron will move up an energy level and is now in it's 'Excited State'.
Photon Emission:
As the electron falls back down to it's ground state a photon is emmited with energy dependant on the energy difference between energy levels.
EACH ENERGY LEVEL HAS DISCRETE ENERGIES!!!!
The energy of the photon emmited corrosponds to a frequency that we can find using E=hf. This frequency then corrsponds to wavelength. This wavelength corrosponds to different sections of the EM spectrum or to a specific color if within range of the visible light.
This is the end of the topic
