OCR 21st Century P2

Radiation and Life
1. Communications
  1. electromagnetic radiation of some frequencies can be used for transmitting information since:
    1. some radio waves and microwaves are weakly absorbed by the atmosphere so can be used to carry information for radio and TV programmes
    2. light and infrared radiation can be used to carry information along optical bres because the radiation travels large distances through glass without being significantly absorbed
    3. Information can be superimposed onto an electromagnetic carrier wave, to create a signal. Carrier wave + information= signal
      1. Analogue signal- a signal which can vary continuously
      2. Digital Signal- a signal that can take only a small number of discrete values (usually two: 1/0)
        this coded information can be carried by switching the electromagnetic carrier wave off and on to create short bursts of waves (pulses) where ‘0’ = no pulse and ‘1’ = pulse
        sounds and images can be transmitted as a digital signal using a code of 1's and 0's
        when the waves are received, the pulses are decoded to produce a copy of the original sound wave or image
        the amount of information needed to store an image or sound is measured in bytes (B)
        Advantages of Digital signals
        can be processed by microprocessors (in mobile phones or computers
        can be stored in memories that take up little space
        generally, the more information stored the higher the quality of the sound or image
        can carry more information per second
        delivered with no loss of quality
        All signals weaken as they travel. Noise ('interference') gets added in.
        A noisy analogue signal carrying music might sound blurry, scratchy and distorted
        Whereas the noisy digital signal is passed through a regenerator (electrical circuit that removes the noise). It can do this because the value is either 0 or 1. A value close to 0 is corrected to 0, a value close to 1 is corrected to 1.
        If you amplify an analogue signal, the noise is amplified too.
Electromagnetic Radiation
1. What is it?
  1. all types of electromagnetic radiation travel at the speed of light (through a vacuum, 300 000 km/s)
  2. A source emits radiation
    1. the radiation travels outwards from the source and can be reflected, transmitted or absorbed (or a combination of these) by materials it encounters
      1. radiation may affect another object (a detector) some distance away, when it is absorbed
    2. This electromagnetic radiation transfers energy in ‘packets’ called photons
      1. the higher the frequency of an electromagnetic radiation, the more energy is transferred by each photon
        The photons of gamma rays transfer the most energy
2. Beams
  1. the energy arriving at a square metre of surface each second is a useful measure of the ‘intensity’ of a beam of EM radiation
    1. the energy transferred to an absorber by a beam of electromagnetic radiation depends on:
      1. the intensity of a beam of electromagnetic radiation decreases with distance from the source because
        the ever increasing surface area it reaches
        its partial absorption by the medium it travels through
      2. the number of photons arriving
      3. the energy of each photon
3. Ionisisng radiation
  1. caused by high energy UV, X-ray and Gamma Radiation
    1. they have a high enough photon energy to remove an electron from an atom or molecule (ionisation)
      1. Ionising radiation can easily kill cells, and can also cause cancer by damaging the DNA in the nucleus of a cell.
Health & Safety
1. The longer the time of exposure, the more radiation is absorbed so the greater the chance of damage to cells
  1. intensity decreases as radiation spreads out from the source
2. Microwaves
  1. microwaves are strongly absorbed by water molecules and so can be used to heat objects containing water
    1. hence their use in microwave-ovens
      1. metal cases and door screens of microwave ovens reflect or absorb microwave radiation and so protect users from the radiation
    2. Mobile phones use microwaves to send signals to the nearby phone mast. When you make a call your skull absorbs most of the microwaves but some reach your brain and warms it ever so slightly, however, the evidence for this is disputed as vigorous exercise has a greater heating effect
3. Ionising
  1. some radioactive materials emit ionising gamma radiation all the time
    1. with increased exposure to ionising radiation, damage to living cells increases eventually leading to cancer or cell death
4. Ozone & UV
  1. In the upper atmosphere some oxygen molecules combine in threes to make ozone
    1. the ozone layer absorbs ultraviolet radiation, emitted by the Sun, producing chemical changes in that part of the atmosphere
      1. When UV radiation is absorbed, its energy can break ordinary oxygen molecules, making 2 free atoms of oxygen. One of these free atoms combines with another 02 molecule to form an ozone (O3) molecule
        This change is reversible as ozone molecules can be split into an oxygen molecule and an oxygen atom is it absorbs enough UV radiation
        the ozone layer protects living organisms from some of the harmful effects of ultraviolet radiation
        sun-screens and clothing can be used to absorb some of the ultraviolet radiation from the Sun
physical barriers absorb some ionising radiation, for example: X-rays are absorbed by dense materials so can be used to produce shadow pictures of bones in our bodies or of objects in aircraft passengers’ luggage, and radiographers are protected from radiation by dense materials such as lead and concrete
Global Warming
1. all objects emit electromagnetic radiation with a principal frequency that increases with temperature
  1. the Earth is surrounded by an an atmosphere which allows some of the electromagnetic radiation emitted by the Sun to pass through. This warms the Earths surface when absorbed.
    1. the radiation emitted by the Earth, which has a lower principal frequency than that emitted by the Sun, is absorbed or reflected back by some gases in the atmosphere
      1. this keeps the Earth warmer than it would otherwise be and is called the greenhouse effect
        Carbon Dioxide, Methane, Water Vapour are examples
2. For thousands of years, the levels of CO2 were stable. Plants absorbed CO2 during photosynthesis, then animals and decomposers returned it to the atmosphere during respiration. Humans did burn wood but that was balanced by new trees growing
  1. The industrial revolution meant that more fossil fuels were burnt, releasing carbon dioxide more than was replaced. Now we rely on electricity for daily needs meaning more fossil fuels need to be burnt e.g. cars, manufactured goods, clean running water etc.
    1. some organisms remove carbon dioxide from the atmosphere by photosynthesis (eg green plants) and many organisms return carbon dioxide to the atmosphere by respiration as part of the recycling of carbon. when animals die, they are decomposed and release any stored CO2.
    2. This is why the amount of carbon dioxide in the atmosphere has been steadily rising
      1. cutting down or burning forests to clear land
      2. burning increased amounts of fossil fuels as an energy source
3. computer climate models provide evidence that human activities are causing global warming
  1. Effects of Global Warming
    1. it being impossible to continue growing some food crops in particular regions because of climate change
    2. more extreme weather events, due to increased convection and larger amounts of water vapour in the hotter atmosphere
      1. flooding of low lying land due to rising sea levels, caused by melting continental ice and expansion of water in the oceans.

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OCR 21st Century P2

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	Creado por Pritesh Patel hace más de 8 años