12.1 - The nature of EM waves

12.1 - The nature of EM waves

1. G.1.1 - EM radiation

   • Radio waves - created by passing alternated current through a wire
   • Light wave - created from the electrons in an atom as they drop from high energy level to low
   • High-frequency waves (UV-light, x-rays, gamma-rays) - created by the nucleus of atoms

2. G.1.2 EM Spectrum

   • Radio waves - Alternating current in an electrical circuit
     • Frequency: 10^8 - 10^9
     • Used in communications
   • Microwaves - oscilliations of electrons in vacuum
     • Used in heating food due to microwaves having a frequency similar to that of water molcules
     • Frequency: 10^9 - 10^11
   • Infrared - energy released by atoms that give up heat
     • Frequency: 10^13 - 10^14
     • Used in TV remote controls, optical insutrments
   • Visible light - photons released by electrons de-exciting
     • Frequency: 10^15
     • Voilet: 380-450 nm
       • Blue: 450-495 nm
         • Green: 495-570 nm
           • Yellow: 570-590 nm
             • Orange: 590-620 nm
               • Red: 620-750 nm

3. G.1.3 - Dispersion

   • The angle of refraction is dependent on the wavelength of the radiation
     • 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!

4. G.1.5 - Physical properties of EM radiation

   • 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.
   • 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.
   • 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.

5. G.1.7 - Lasers

   • 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
   • 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.
     • Both are needed in lasers!
       • Creating a laser
         • 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.
       • Uses of lasers
         • - Some fancy outlining of a use of lasers.