The wave particle duality theory states that light behaves as a particle AND a wave at the same time.
Light as a Wave
- Interference 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 quatised 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
The Planck's constant is provided in As/A-level Physics exam paper!🚨
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 Absorption and Emission
Photon Absorption:
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 emitted with energy dependent on the energy difference between energy levels.
EACH ENERGY LEVEL HAS DISCRETE ENRGIES!!!!
The energy of the photon emitted corresponds to a frequency that we can find using E=hf. This frequency then corresponds to wavelength. This wavelength corresponds to different sections of the EM spectrum or to a specific color if within range of the visible light
References:
https://community.asdlib.org/imageandvideoexchangeforum/2013/07/26/absorbance-and-emission-spectroscopy/
https://phys.org/news/2015-08-ultrafast-electron-diffraction-reveals-rapid.html
This is the end of the topic!
Drafted by Cherry (Chemistry)