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Electromagnetic radiation

  • all waves in the electromagnetic spectrum transmit through a vacuum at 300,000km/s
  • the energy of a wave in the spectrum increases with increasing frequency, waves with higher frequencies carry more energy
  • radiowaves-microwaves-infrared-UV-X-rays-gamma rays
  • electromagnetic waves transfer energy in packets called photons
  • the energy in a photon depends only on the frequency of the wave, increasing the frequency of the wave increases the energy of its photons
  • the energy absorbed in each second from an electrogmagnetic wave depends on its intensity
  • the intensity of a wave decreases with increasing distance from its source
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  • Atoms and molecules have no overall electric charge
  • Electrons are negatively charged
  • Ions are either positive or negatively charged
  • X-rays and gamma rays are ionising radiation
  • ionisation of a molecule can trigger a chemical reaction involving that molecule
  • cells are ionised and damaged when they absorb gamma or x rays, the damaged cells die or develop into cancer
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  • things which absorb radiation heat up
  • cells which absorb radiation are damaged if they get too hot
  • water molecules are good at transferring energy in microwaves to thermal energy
  • they are used in microwave ovens, and mobile phones
  • the health risks of micro waves is very small but people are concerned
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  • sunlight contains UV radiation
  • UV radiation causes sunburn and skin cancer
  • a layer of Ozone at the top of the atmoshphere absorbs UV radiation from the sun
  • this protects living things on Earth from some of the harmful effects of UV radiation
  • UV radiation from the sun causes chemical changes to molecules in the ozone layer
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Greenhouse effect

  • radiation from the sun comtains a range of frequencies
  • only some of those frequencies can pass through the atmosphere of the Earth
  • the Earth warms up when it absorbs radiation from the sun
  • the infrared radiation emitted by the Earth makes it cool down, radiation from the Earth may pass into space, reflect off clouds, or radiate back from gases which absorb it
  • When the Earths radiation is absorbed or reflected back, this keeps the Earth warmer this is called the greenhouse effect
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Carbon dioxide in the atmosphere

  • Carbon is found in all living things
  • Carbon dioxide in the atmosphere is found in very small amounts, it is absorbed by plants through photosynthesis and released by living organisms as they decompose and respire
  • carbon dioxide is one of the main greenhouse gases found in the Earths atmosphere
  • the level of carbon dioxide has steadily increased due to the burning of fossil fuels and deforestation
  • the increase in the Earths temperature correlates with the rise in carbon dioxide levels in the Earths atmosphere
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Global Warming

  • the greenhouse effect is slowly increasing the average temperature worldwide, this is called global warming
  • various gases in the atmosphere are responsible for the greenhouse effect: water vapour, carbon dioxide, and methane
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Electromagnetic waves for communication

  • some electromagnetic waves can carry information from one place to another, including text voice music and pictures
  • radiowaves and microwaves are not absorbed by air this means they can carry radio and TV broadcasts through the atmosphere
  • infrared and light are not easily absorbed by the glass of optical fibres, this means they can be used for long-distance telephone and internet communication
  • radiowaves use a carrier wave to transfer information, this information is used to change the amplitude or frequency of the carrier in a process called modulation
  • a radio reciever demodulates the carrier wave to recover the information
  • an analogue signal varies continuously with any value, sound is an example
  • modulation which varies the amplitude of a radio wave continuously makes analogue signals
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Digital signals and information

  • a digital signals has only a few values. the digital code for sending sound of pictures has only two values, 1 and 0
  • analogue signals vary continuously
  • analogue signals can be sent by a radio wave in a digital code, the value of the signal is measured and coded as a string of 1s and 0s
  • the 1s and 0s make a digital signal by pulsing the carrier wave on and off 
  • radio recievers use the strings of 1s and 0s in the digital signal to recover the orgional analogue signal and produce a copy of it
  • radio waves can be affected by noise
  • digital information is stored as bytes
  • a byte is a string of 8 binary digits, each binary digit can be either 1 or 0
  • digital information builds up images from many small dots called pixels 
  • increasing the number of binary digits for a picture increases the sharpness of the image
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