Core Physics - Topic 2 Electromagnetic Spectrum

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  • Created by: Katie
  • Created on: 10-04-13 19:04

Beyond The Visible

  • William Hershel (1738-1822)
    • Different coloured filters heated up his telescope to different extents
    • Did different colours of light contained different 'amounts of heat'?
    • Split sunlight into a spectrum using a pyramid
    • Put a themometer at each colour & saw temperature rise
    • Measured beyond the red end of the spectrum
      • no visible light
      • highest temperature of all
      • INFRARED waves/radiation
  • Johann Ritter (1776-1810)
    • aimed to find 'invisible rays' at the violet end of the spectrum
    • used silver chloride chemical
    • turned black fastest when exposed to 'invisible rays' beyond violet
    • ULTRAVIOLET waves/radiation
  • Electromagnetic radiation - visible light, infrared and ultraviolet
  • Transfer energy from one place to another
  • Electromagnet vibrations are right angled to the direction of the waves - traverse waves
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The Electromagnetic Spectrum

  • Electromagnetic waves travel without any particles to vibrate
  • Move easily through a vacuum e.g. space
  • Travel at 300,000 km/s in a vacuum
    • fastest speed anything can come
  • Colour of visible light depends on wavelength
  • Light waves longer than red lights - humans can't see
    • e.g. infrared, microwaves and radiowaves
  • Shorter wave lengths mean high frequencies
    • higher frequency than visible light
    • e.g. ultraviolet, X rays and gamma rays
  • The Hubble Space telescope detects visible light, UV and IR
  • Radio and X-ray astronomy have developed relatively recently
  • (
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Electromagnetic Dangers

  • Mobile phones use microwaves but at a different frequencies to microwave ovens
    • scientists say mobile phone use doesn't cause a health risk
  • Microwave ovens use a certain frequency that heats water
    • danger to humans because our bodies are mainly water
  • IR radiation used in grills and toasters to cook food
  • Our skin absorbs IR which we feel as heat
    • too much can destroy cells causing burns to skin
  • Higher frequency transfer more energy - more dangerous
  • Sunlight contains UV - carries more energy than visible radiation
  • UV transferring to our cells can damage their DNA
    • can damage skin cells so much that it can lead to skin cancer
  • UV can also damage our eyes
    • skiers/mountaineers suffer from temporary 'snow blindness'
  • X-rays and gamma rays can penetrate the body
    • excessive exposure may cause mutations in DNA killing cells and causing cancer
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Using Electromagnetic Radiation

  • EURion pattern on banknotes can be seen when illuminated
    • reflect certain wavelengths of visible light
  • Security markings on banknotes can't always been seen
    • fluorescence absorbs UV light and re-emit visible light
  • Fluorescent lamps produce UV waves, use a fluorescent material inside
  • X-ray scanners used in airports to detect hidden objects
  • All warm objects give off some heat as IR radiation
  • Radiowaves and microwaves carry TV signals
  • Radiowaves carry Wi-Fi signals
  • Microwaves carry mobile phone signals
  • IR waves carry short distance signals like remote to TV
  • IR waves sent down optical fibre cables for telephone and internet
  • UV light kills bacteria - disinfect water and sewage
  • Gamma rays kill cells - used to sterilise
  • Gamma rays detect and kill cancer cells in radiotherapy
    • chemical that emits gamma rays injected into the blood
    • collects inside cancer cells and are decteted and located by a scanner
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Ionising Radiation

  • Gamma rays increase cancer risk by causing mutations to cell's DNA
    • because they are ionising radiation
  • Ionising radiation can remove electrons from atoms to form ions
    • ions are very chemically reactive
    • DNA damage if atoms in the cell are ionised
  • More exposure = more destroyed cells
  • Elements like radium naturally emit gamma waves
    • therefore radioactive
  • Some radioactive substances emit alpha and beta particles
  • All types of ionising radiation
    • transfer energy from the radioactive material to surroundings
  • Alpha and beta particles are not electromagnetic radiation
  • They are particles of matter that are emitted with lots of kinetic energy
    • the energy can ionise atoms
  • So they are also potentially hazardous to life and damage DNA in cells
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