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Electromagnetic waves
EM radiation can be absorbed, reflected or transmitted
· The radiation can be transmitted- just passes through the substance
· It could be reflected-bounces back
· It is absorbed- the energy is transferred to the matter
when the EM radiation has two effects:
· Substances gets hotter
· It sets up a tiny alternating current with the same frequency
Some radiation are more harmful then others
· What effect radiation has depends on what type it is and the size of the dose you get
Radio waves are used mainly for communication
· The radio wave used for TV and FM radio
· To get reception you must be in direct sight of the transmitter
· Short radio signals can be received at long distances, that because they are reflected
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Microwaves
Microwaves are used for satellite communication
· For satellite TV from a transmitter is transmitted into space where its
picked up by satellite receiver dish orbiting. The satellite transmit the
signal back to earth in a different direction where its received by a
satellite on the ground. Mobile phone use the similar way and
remote-sensing
Optical fibres use visible light or infrared
· Optical fibres can carry data over long distances as pulse of light
and infrared
· They work by bouncing off the insides of the thin inner core of glass
and plastic and is reflected and repeated
· Optical fibres work because of total internal reflection
· It only happens in dense materials
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Hazards of EM radiation
Higher frequency EM radiation is usually more dangerous
· This is because the energy of any electromagnetic wave is directly proportional to it
frequency. So the higher the frequency wave have more energy. The more energy
the more damage
· microwaves- may or may not be harmful
· Some wavelengths of microwaves are absorbed by water molecules and heat them
up. If the water in question happen in your cells, you might start to cook
Ultraviolet can cause skin cancer
· You can get skin cancer if you spend a lot of time in the sun. this is because sun rays
include radiation which damages the DNA
· Dark skin give you some protection because it absorbed the heat
X-rays are used in hospitals but are pretty dangerous
· Radiographers in hospitals take x-ray photographs to help doctors diagnose broken
bones. X-rays pass through flesh but not bones
· X-rays lead to mutation this cause cancer
· Patients are often protect other parts of the body which are not being investigated
therefore reducing the chances of cancer
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Analogue and digital signals
Information is converted into signals
· For instance, sound and pictures are converted into electrical signals before being transmitted
Analogue signals vary but digital either switch on or off
· The amplitude of analogue and frequency vary continuously. It can take any value in a particular
range. Thermostat are analogue devices
· Digital signals are coded pulse, they only take two values (on/off) Digital clocks are digital devices
Signals have to be amplitude
· Both analogue and digital signals weaken so they need to be amplitude
Digital signals are better quality
· Noise is less of a problem with digital signals, if you receive a noisy digital signals, its pretty
obvious what it suppose to be. The digital signals are much higher quality as the information
receive remains the same
· Digital signal are also easy to process using computers since computer are digital devices
· An advantage is it can transmit several signals at once- so you cab send more information
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Radioactivity
Nuclei contains protons and neutron, it makes up most of the mass of the atom
· Electrons are negatively charged and are really small
· Isotopes are atoms with different number of neutrons
Radioactive decay is a random process
· The nuclei of unstable isotopes break down at random
· Each nucleus just decays spontaneously in its own time. Its completely
unaffected but physical conditions like temperature
When the nucleus does decay it spits out one more of the three types of
radiation
· Alpha
· Beta
· Gamma
· In the process the nucleus often changes into a new element
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