P2 - RADIATION AND LIFE

P2 - RADIATION AND LIFE

1. ELECTROMAGNETIC SPECTRUM

   • family of seven radiations
     • low energy photons
       • radio waves
         • microwaves
           • infrared rays
             • Visible spectrum
               • Ultraviolet rays
                 • X-rays
                   • Gamma rays
                     • High energy protons
   • a beam of electromagnetic radiation contains 'packets' of energy called photons
   • the higher the frequency of electromagnetic radiation the more energy is transferred by each photon
     • all electromagnetic radiation travells at the same finite speed of 300,000 km/s through a space vacuum.

2. TRANSMITTING RADIATION

   • energy travels from a source that emits radiation to a detector that absorbes it
   • on journey fro emitter to detector, materials can transmit, reflect or absorb
     • eg clouds absorb and reflect the suns energy - on cloudy day get less sunlight
   • see book pg 74

3. INTENSITY AND HEAT

   • intensity of electromagnetic radiation is the energy arriving at a square meter per second
   • depends on number of photons delivered per second and amount of energy each packet contains (photon energy)
   • intensity decreased with distance
   • when material absorbs radiation heat is created
     • amount of heat depends on the beam intensity and / or duration of exposure
   • decrease in intensity of radiation due to 3 factors
     • photons spread out as travel
     • photons absorbed by particles in substances they pass through (dust in cloud)
     • some photons reflected and scattered by other particles
     • see diagram pg 75
     • these factors combine to reduce number of photons arriving per second at detector = lower measured intensity

4. IONISING RADIATION

   • this is electromagnetic radiation with high energy photons.
     • can break molecules into bits called ions
       • ions are very reactive and can easily take part in other chemical reactions
   • ultraviolet, X-rays and Gamma rays are examples of ionising radiation
   • Ionising electromagnetic radiations have high enough photon energy to remove an electron from an atom or molecule

5. CELL DAMAGE

   • radiation damages living cells in different ways
     • heating effect can damage skin eg sunburn
       • ionising radiation can age skin and mutate dna = cancer
         • different amounts of exposure can cause different effects.e.g high intensitity ionising radiation can distroy cells leading to radiation poisioning
   • microwaves - can heat materials by causing water particles to vibrate
     • there may be a health risk from low intensitity microwaves from mobile phone and masts
       • this is disputed
   • see diagram pg75

6. RADIATION PROTECTION

   • microwave ovens have metal case and wire screen in door to stop too much radiation escaping
   • other physical barriers to protect people are;
     • lead screens - X rays
     • sun screens and clothes - ultraviolet radiation prevent skin cancer
     • nuclear reactors encased in thick lead and concrete
   • some radioactive materials emit ionising radiation all the tme - radiation suites worn as shield and a radiation dose monitor

7. THE SUN AND THE OZONE LAYER

   • all objects emit electromagnetic radiation with frequency that increases with temperature
   • light radiation from sun warms earth when absorbed - used by plants - photosynthesis
   • photosynthesis counteracts respiration by removing carbon dioxide and adding oxygen
   • ozone layer is thin layer of gas in earths upper atmosphere. absorbs some of suns ultraviolet radiation before reaches earth
   • without ozone layer too much radiation would reach earth most animals suffer cell damage
   • energy from ultra violet radiation causes chemical changes in upper atmosphere when absorbed by ozone layer - reversible

8. THE GREENHOUSE EFFECT

   • earth emits electromagnetic radiation into space
   • gasses in atmosphere absorb some of radiation- keeps earth warmer than would otherwise be - greenhouse effect
   • atmosphere only allows some electromagnetic radiation from sun to pass through
   • carbon dioxide (greenhouse gas) makes up small amount of atmosphere - this is rising over last 200 years
   • other greenhouse gasses are - water vapour and trace amounts of methane
   • radiation emitted by earth has a lower principle frequency than the sun
   • see diagram pg 76

9. THE CARBON CYCLE

   • SEE DIAGRAM PG 77
   • USING THE CARBON CYCLE
     • carbon cycle can be used to explain some points
       • carbon dioxide levels in atmosphere remained the same for 1000's years as always recycled by plants and animals
       • decomposers are important micro organisms that break down dead material and release CO2
       • CO2 levels steadily increasing du to human activity - burning fossil fuels and de-forestation
       • burning fossil fuels releases carbon that was removed by atmosphere millions of years ago
       • deforestation (burning) releases carbon and removes number of plants removing CO2 from atmosphere

10. GLOBAL WARMIING

    • increase in greenhouse gasses causes rise in amount of radiation from sun absorbed by atmosphere - causes earth to heat up = global warming
    • problems include - climate change (crops cannot grow some area)
      • extreme weather - hurricanes
      • rising sea levels - ice caps melt and rising sea temps - low lying areas flood
    • data on earths changing temp is used with climate models to find patterns for possible causes of global warming
      • these models show main global warming factors is rise in CO2 in atmosphere proving humas to blame
        • increased convection and larger amounts of water vapour in hotter atmosphere result in extreme weather events.

11. ANALOGUE SIGNALS

    • information can be superimposed into electromagnetic carrier wave to create a signal
    • amplitude modulation (AM) or frequency modulation (FM) - amplitude or frequency of the carrier wave is changed by the input signal
    • with frequency modulation (FM) of the input signal causes frequency of carrier wave to change
    • in both cases the signal is called an analogue signal as it varies in the same way as the information it is carrying
    • analogue signals can have almost any value
    • see diagram pg 78

12. USES OF ELECTROMAGNETIC WAVES

    • different electromagnetic waves have different frequencies
    • can be used for different purposes depending on how much they reflect, absorb or transmitted by different materials
    • signals can be carried by radio waves and micro waves through atmosphere and space
    • light and infra red waves through optical fibres
    • radio waves - used to transmit radio and television as not strongly absorbed by atmosphere
    • microwaves- reflected well by metals (satalite dishes) - some frequency strongly absorbed by water molecules so used to heat items with water content
      • some are not strongly absorbed by atmosphere so can carry TV and radio signals
    • visible light and infra red- travel huge distancesdown optic fibres without becoming weaker - useful for carrying information- easily boosted at intervals along optic fibre
    • X-rays - absorbed by denser materials - produce shadow pictures of bones and inside luggage at airports

13. DIGITAL SIGNALS

    • info including sounds can be transmitted digitally
    • signal created into digital code uses 0 (off) 1(on) turned into short bursts of waves called pulses
      • pulses produced by switching electromagnetic carrier wave on and off
      • when digital signal recieved pulses are decoded to produce copy of original sound wave or image

14. BENEFITS OF DIGITAL SIGNALS

    • digital and analogue signals
      • become weaker (amplitude smaller) as they travel - may be amplified at selected intervals
      • can pick up random variations called noise = reduces quality of sound
      • digital signals travel long distance at higher quality than analogue - due to
        • analogue can have many different values so hared to tell if 'noise' or original signal
          • noise can never be completely removed
        • digital signals only have 2 states - on or off so can be recognised dispite any 'noise'picked up
          • interferences can be removed
            • signal can be regenerated without the noise
    • when signal amplified any noise also amplified

15. STORING INFORMATION

    • bit - piece of info either 1 or 0. Byte = 8 bits of info
    • in digital mobile phone picture each pixel needs 8 bits or 1 byte of info
      • more pixels = more bytes = higher quality of picture
    • picture stored on memory card - info stored measured in bytes
    • digital music stored on CD in form of bytes - series of pits read by lazer as 1 (bit) arranged in a spiral on the surface.
      • in between are flat surfaces read as 0. series of bits converted to analogue form to give high quality signal.

16. USING DIGITAL INFORMATION

    • the advantage of transmitting information using digital signals is that
      • info stored on hard drive, CD, DVD, memory stick
      • info processed by computer - eg for spell check, photo editing, music editing
    • digital pictures
      • use photo editing software to manipulate pictures
      • store on hard drive , CD or memory stick
      • music in MP3 / WAV format
        • remove noise, amplify and edit signals
        • store on hard drive CD or Memory stick