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- Created by: Elliemcgowanx
- Created on: 03-05-14 13:13
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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Ionisation
- 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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Microwaves
- 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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Ozone
- 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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