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  • Created by: Dr Afzal
  • Created on: 24-01-10 12:12

Electromagnetic Waves

Wave speed=

Frequency

x

Wavelength

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Electromagnetic Waves

EM Radiation can be:

Transmitted- pass through the substance

Reflected- bounce back

Absorbed- enerfy of wave is transfered through matter

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Electromagnetic waves

Radio Waves:

Long radio wavelengths: 1-10km:

Bend around the curved surface of the Earth

Can also get around hill, into tunnels etc

Used for TV and FM radio

Short radio wavelenths: 10cm-10m:

Be recieved lond distances by transmitter

Reflected from ionsphere

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EM Radiation

Microwaves:

Communication to and from satellites but you need to use microwave signals which pass easily through earth's watery atmosphere

For satellite TV, the signal from a transmitter is transmitted into space

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EM Radiation

Optical fibres:

Can carry data over long distances as pulses of light or infrared radiation

Work by bouncing waves of the sides of a thin core of glass or plastic

Optical fibres work because of total internal reflection

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Higher frequency usually more dangerous

Higher frequency waves have more energy- enerygy of wave does damage

visble light isn't harmful unless really bright

Infrared can cause burns or heatstroke

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Microwaves

Some wavelengths of microwaves are absorbed by water molecules and heat them up

If water molecules reach skin- skin could start to cook

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Ultraviolet

Ultarviolet radiation damages DNA in your cells- Causes skin cancer

Dark skin- protects against UV rays because absorbs more vulnerable tissues deeper in the body

If you have pale skin and your in the sun you need to take extra care

The gas inside fluorescent tubes emits Ultraviolet radiation

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X-Rays

X-rays easily pass through flesh but not through denser material like bones or metal

X-rays can cause mutations which can lead to cancer

Lead aprons minimise exposure to X-rays

Lead shields are given to the parient on parts of body where they don't want x-rays

Pregnant women shouldn't have X rays

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Analogue and Digital Signals

Information such as sounds and pictures is converted into electrical signals

Amplitude and frequency of an anlogue signal vary continously

Old fashion watches, thermometers- Analoge devices

Digital Signals only take 2 values (on or off)

Signals pick up interference or noise from electrical disturbances or other signals

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Digital signals are better quality

Noise is less problem with digital signal

If you amplify a noisy anologue signal, you'll amplify the noise as well

Digital signal, the signal is recieved same as the original

Digital signals easier to process with computers

With Digital technology you can transmit several signals at once using just one cable or EM wave

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Radioactivity

Nucleus contains protons and neutrons (make up most mass of atom)

Electrons are negatively charged and really really small- paths take up a lot of space

The word "ATOM" was being bandied around over 2400 years ago by a greek philosopher, Democritus

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Radioactivity- Isotopes

Isotopes are atoms with the same number but different number of protons

Usually each element has only one or two stable isotopes

The other isotopes tend to be radioactive- the nucleus is unstable, so it decays (breaks down) and emits radiation

AND RADIOACTIVE DECAY BREAKS DOWN SPONTANEOUSLY IT'S UNAFFECTED BY ANYTHING ELSE IT'S A RANDOM PROCESS

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Radioactive decay is a Random process

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Radioactivity- Nuclear Radiation and Alpha particl

Nuclear Radiation causes ionisation, by bashing into atoms and knocking electrons off them, atoms are turned into ions

Alpha particles are big, heavy and slow moving

Because of their size they bash into a lot of atoms and electrons off them, before they slow down

Alpha particles are deflected by electric and magnetic fields

Alpha particles are electrically charged with a positive charge

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Beta Particles

A beta particle is an electron which has been emitted from the nucleus of an atom when a neutron turns into a proton and an electron

Move quite fast and are quite small

Negatively charged- deflected by electric and magnetic fields

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Gamma Rays

Gamma rays have no mass- just energy

Penetrate a long way into materials without being stopped

This means they are weakly ionsing- tend to pass through rather than collide with atoms

Gamma rays have no charge

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Alpha, Beta, Gamma

Alpha particles blocked by pape, skin or few mm of air

Beta particles stoppes by thin metal

Gamma rays are blocked by thick lead or very thick concrete

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Half Life

HALF TIME IS THE TIME TAKEN FOR HALF OF THE NUCLEI NOW PRESENT TO DECAY

A short half life means the activity falls quickly, because lots of nuclei decays quickly

A long half life, activity more slowly because most of nuclei don't decay for long time

You can work out the hallf life of a sample by monitoring its count rate (the number of atoms which decay per minute)

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Uses of Radiation

Gamma radiation- Sterilise machines and kill bacteria on medical instruments and find underground leaks of pipes

Smoke detectors use a weak source of alpha radiation to ionise the air between two electrodes

A source of with a fairly long half-life is used so detector will work for many years

Beta and gamma radiation will penetrate skin and other body tissues

So it's injected or just swallowed

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Risks of Radiation

Beta and Gamma sources, however are less dangerous inside the body because they pass thorugh the body without causing damage

If radiation enters body it will collide with molecules in cells- collision causes ionisation

Higher doses tend to kill cells completely

Radiotherapy is used to kill cancer (gives high dose of gamma rays)

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Comments

Mindy van Daal

GCSE Russian?! Not quite. I suggest recategorising.

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