Physics P1b

Radiation and the Universe

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  • Created by: Moog
  • Created on: 16-10-10 14:39

The Electromagnetic Spectrum

  • The electromagnetic spectrum, (in order of increasing wavelength); gamma rays, x-rays, ultraviolet, visable, infar-red, microwaves, radiowaves
  • All electromagnetic waves travel at the same speed in space (300million m/s)
  • Wave speed= frequency x wavelength

 

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Gamma Rays and X-rays

  • X-rays and gamma radiation are absorbed by dense materials in bone and by metal
  • X-rays and gamma radiation damage living tissue when they pass through it
  • X-rays are used in hospitals to radiographs
  • Gamma rays are used to kill harmful bacteria in food, to sterilise surgical equipment and to kill cancer cells
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Light and Ultraviolet Radiation

  • Ultraviolet radiation is in the electromagnetic spectrum between violet light and X-radiation
  • Ultraviolet radiation has a shorter wavelength than viable light
  • Ultraviolet radiation can harm the skin and the eyes
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Infra-red, microwaves and radio waves/Communicatio

  • Infra-red:Heaters, communication (remote handsets, optical fibres)
  • Microwaves: Microwave oven, comminications
  • Radio waves: Communications
  • Communications- the use we make of the radio waves depend on the frequency of the waves, Visible light and infra-red radiation are used to carry signals in optical fibres
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Analogue and Digital Signals

  • Analogue signals vary contiously in amplitute
  • Digital signals are either high (1) or low (0)
  • Digital transmission, when compared with analogue transmission is free of noise and distortion. It can also carry much more information

 

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Observing Nuclear Radiation

  • A radioative substance contains unstable nuclei
  • An unstable nucleus becomes stable by emitting radiation
  • There are three main types of radiation from radioactive substances-Alpha, Beta and gamma radiation
  • Radioactive decay is a random event-we cannot predict or influence when it will happen


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Alpha, Beta and Gamma Radiation

  • Alpha radiation is stopped by paper or a few centimetres of air
  • Beta radiation is stopped by thin metal or about a metre of air
  • Gamma radiation is stopped by thick lead and has an unlimited range in air


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Half-life

The half-life of a radioactive substance is the time it takes:

  • for the number and (therefore the mass) of parent atoms in a sample to halve
  • for the count rate from the original substance to fall to half its initial level
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Radioactivity at Work

The use we can make of a radioactive substance depends on: 

  • its half-life and 
  • the type of radiation it gives out
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The Expanding Universe

  • Light from distant galaxy is red-shifted to longer wavelengths
  • The further away the galaxy the bigger the red shift
  • Red shift provides evidence that the univercse is expanding
  • The universe started with the Big Bang, a massive explosion from a very small point

 

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Looking into Space

  • Observations are made with telescopes that may detect visible or other electromagnetic radiations
  • Observations of the Solar System and galaxies can be carried out from the Earth or from space
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