12.1 - The nature of EM waves

G.1.1 - EM radiation
1. Radio waves - created by passing alternated current through a wire
2. Light wave - created from the electrons in an atom as they drop from high energy level to low
3. High-frequency waves (UV-light, x-rays, gamma-rays) - created by the nucleus of atoms
G.1.2 EM Spectrum
1. Radio waves - Alternating current in an electrical circuit
  1. Frequency: 10^8 - 10^9
  2. Used in communications
2. Microwaves - oscilliations of electrons in vacuum
  1. Used in heating food due to microwaves having a frequency similar to that of water molcules
  2. Frequency: 10^9 - 10^11
3. Infrared - energy released by atoms that give up heat
  1. Frequency: 10^13 - 10^14
  2. Used in TV remote controls, optical insutrments
4. Visible light - photons released by electrons de-exciting
  1. Frequency: 10^15
  2. Voilet: 380-450 nm
    1. Blue: 450-495 nm
      1. Green: 495-570 nm
        Yellow: 570-590 nm
        Orange: 590-620 nm
        Red: 620-750 nm
G.1.3 - Dispersion
1. The angle of refraction is dependent on the wavelength of the radiation
  1. This means that light of different wavelengths (coulours) does not bend equally much; as white light passes through a prism the blue light is bent more than the red light etc., and you will have a pretty rainbow!
G.1.5 - Physical properties of EM radiation
1. Transmission- when a wave does not have the correct frequency to interact with the atoms of a substance, the energy is sent away again, it is transmitted.
2. Absorption- when a wave does have the right frequency to interact with atoms of a substance, it gives energy to the electrons and excites them. The electrons has thus absorbed the energy.
3. Scattering- when a wave is forced to change direction due to small particles of e.g. water is in the way. The wave is sent off in a different direction, and is thus scattered.
G.1.7 - Lasers
1. Monochromatic light- light in which all photos have the same wavelength and therefore the same colour. This is why lasers always come in one colour only; the light is monochromatic
2. Coherent light- light in which all photons are released in the same direction and in phase. This is why lasers are beams of intense light and not, for example, a light bulb.
  1. Both are needed in lasers!
    1. Creating a laser
      1. Population inversion is when a flash of light excites atoms, so there are more atoms withing the tube that are excited than are not. The atoms get de-excited, so they release photons in a random direction within the tube. When one of these photons pass by still excited photos they de-excite them too, in a sort of chain reaction that amplifies the light.
    2. Uses of lasers
      1. - Some fancy outlining of a use of lasers.

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12.1 - The nature of EM waves

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