Physics P1 - Uses Of Electromagnetic Waves

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Electromagnetic radiation

Is either;

  • Transmitted (passed straight through) an object.
  • Reflected back from the object.
  • Absorbed, this makes the object increase in heat or create an alternating current.

What happens to the waves depend on the wavelength, this is because different types of radiation react differently with different matter.

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Harmful Radiation

Most electromagnetic radiation passes straight through soft cells, but there are some exceptions;

  • Microwaves are absorbed. This causes an object to heat up.
  • Ultra-violet radiation can cause skin cancer usually from the sun.
  • Some types of radiation can destroy cells altogether!
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Radio Waves

  • Radiowaves are normally used for communications. So, they control things like your TV and radio(surprisingly!)
  • There are both long and short distance radio waves.
  • Radiowaves with long wavelengths can be received half way round the Earth and can bend.
  • Radiowaves with short wavelengths can also be received at long distances, this is because they are reflected from the ionosphere.
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Microwaves

  • Microwaves are used for satelillite communication (be sure not to get this mixed up with radiowaves).
  • It includes things like satellite TV signals and satellite phones, although, mobile phones can also use these types of waves.
  • Microwaves pass through the Earth's watery atmosphere easily.
  • They are used by remote sensing satellites which help them to see through the clouds and moniter things more accurately.
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Visible Light and Infra-Red

  • Optical fibres carry data long distances, either as pulses of light or infra-red radiation.
  • They work by reflecting off the inner tube of plastic/glass and coming out of the other side of the tube.
  • Optical fibres work because of total internal reflection.
  • Total internal reflection can only happen when waves pass through a dense substance (like glass or plastic) and move towards a less dense substance (like air).
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X-Rays

  • Radiographers in hospitals take X- rays to examine broken bones. X- rays pass easily through flesh but less easily through bone (or metal!)
  • Although X- rays seem helpful, they can cause cancer!
  • Lead shields are used to protect the radiographer and parts of the pateient that need to be protected.
  • Pregnant women shouldn't have X- rays, her baby is vulnerable and it could cause harm.
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