OCR (Gateway) P4 revision notes - Radiation for life.

notes for P4, short and to the point, includes higher tier requirement knowledge too

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OCR (Gateway) P4 revision notes - Radiation for life.
GENERATING STATIC ELECTRICITY:
Insulating materials can become electrically charged if rubbed with another insulating
material.
Electrons transfer from one material to another, one material will gain a positive charge and
the other will gain a negative charge due to the transfer of electrons. Note that only
electrons can be transferred from a material, protons never do ­ it is the lack of electrons
that cause a material to become positively charged.
Synthetic clothing can become charged due to friction between the clothing and person's
body when clothes are put on. When the clothing is removed from the body, static sparks
are sometimes produced.
DISCHARGING STATIC ELECTRICITY:
Charged objects can be discharged by earthing them.
When an object discharges, electrons are transferred from the charged object to earth.
If you become charged and then earthed, you could get an electrostatic shock.
PROBLEMS OF STATIC ELECTRICITY:
In some situations, static electricity can be a nuisance.
It can cause dirt and dust to be attracted to insulating materials and cause some materials
cling to your skin.
Static electricity can also be very dangerous.
It can be dangerous in any situation where large amounts could flow through your body to
earth, e.g. lightning.
REPULSION AND ATTRACTION:
2 insulating materials with same charge will repel.
2 insulating materials with different charges will attract.
REDUCING THE DANGER:
Receiving an electric shock can be reduced by:
Making sure appliances are correctly earthed,
Using insulation mats
Wearing shoes with insulating soles
Lorries containing inflammable gases, liquids or powders need to be earthed before
unloading. This is because friction causes a build-up of charge which could lead to a spark
which would then ignite the flammable substance.
Anti-static sprays, liquids and cloths help reduce the problems of static electricity by
preventing transfer of charge from one insulator to another.
If there is no build-up of charge, there can't be any discharge.

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USING STATIC IN EVERYDAY LIFE
Photocopiers:
Image of page to be copied is projected onto a positively charged plate
Light causes charge to leak away, leaving electrostatic impression of the page
Charged impression on plate attracts tiny specks of black powder, transfers from
plate to paper
Heat fixes final image on paper.
Defibrillators:
Electricity use to start the heart when stopped,
Two paddles are charged and put in good electrical contact with the patient's chest
Charge is then passed through patient to make heart contract.…read more

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DOUBLE INSULATION:
Appliances with outer metal cases have an earth wire, they are earthed.
An earthed conductor cannot become live.
Some have cases are made of insulators, don't have an earth wire but still have a fuse.
EARTHING:
Electrical appliances with outer metal cases are earthed to protect the appliance and the
user.
The earth wire and fuse work together
1. Fault in appliance causes casing to become live
2. The circuit short-circuits because the earth wire offers less resistance.
3. Fuse wire melts.
4.…read more

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PARTICLE MOTION IN WAVES:
All waves transfer energy from one point to another, without transferring any particles of
matter.
Two types of waves:
Longitudinal Waves- each particle move backwards and forwards about its normal
position , same plane as the direction of wave movement
Transverse waves- each particle moves up and down about it normal position at
90degrees to the direction of the wave movement.…read more

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TRACERS:
Tracers are small amounts of radioactive materials which can be swallowed or injected into a
patient.
Given time to spread through the body, whilst progress is followed using external radiation
detector.
Radioactive material must emit either gamma or beta radiation, both pass through skin, able to
be detected.
RADIOACTIVITY:
Radioactive materials give out nuclear radiation from nucleus of their atoms.
Atoms are unstable and decay naturally.…read more

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BACKGROUND RADIATION:
Occurs naturally in our environment and is all round us.
Most is released by:
Radioactive substances in soil and rocks.
Cosmic rays from outer space.
Some background radiation comes from man-made sources and waste products.
Industry and hospitals both contribute to background radiation levels.
TRACERS:
Radioisotopes are used as tracers in industry and hospitals.Tracers are used to:
Track dispersal of waste
Find leaks and blockages in underground pipes
Find routes of underground pipes.
1.…read more

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FISSION:
Nuclear fission is the process which heat energy is given out in a nuclear reactor.
Decay of uranium can be a chain reaction.
Uranium nucleus absorbs a single neutron, becomes radioactive and splits, releasing heat energy
& more neutrons.
These neutrons cause more uranium nuclei to split, chain reaction continues.
Nuclear bomb is a chain reaction, gone out of control, results in release of one powerful burst of
energy.
Nuclear fission produces radioactive waste, very dangerous.…read more

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