P4 - Revision Cards in GCSE Physics

Current

electrical current=flow of electrons through wire
metals good electrical conductors allow eletrons to flow through
plastic=poor conductor or insulators electrons cant flow easily
insulators become electrically charged when rubbed (friction)
electrons gained= positivly charged, when lost= negitive charged
same charge=repel, different charge= attract
insulator charge builds up, escapes through sparkor electrical current.
prevent charge build up= earth wire
charge can build on humans but cant feel as no moving electrons, feel shock when electrons move from us to something else in current.
Current= flow of electron.

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Dust precipitators, in chimeneys stop soot escaping, charged plate at bottom of chimney, soot passes through and given charge. chimeney= opposite charge, soot attracted, collected and eventually get too heavy and drops and collected.
Paint particles, gain charge at nossle and repel when leave spray,spreads into fine mist, ensures even coating, opposite charge on car= no shadows paint spreads into small gaps.
defibrillators, restart heart. ensure good electrical connection using gel, shave chest so no interference.

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devices have resistance, measure of how difficult for electrons to flow, bigger resistance= smaller current.
The longer or thinner wire= bigger resistance.
resistance= voltage/ current
measured in ohms Ω
resistance= atoms colliding with electrons as they flow, hotter wire get, more atoms vibrate and bigger resistance.

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normal circuit= positive+ negitive wires, in plug called live and neutral wires.
live wire, brown and right side of plug. electrons in wire lots of energy, touching live wire will give shock.
Fuse to live wire melts when current flows too big. breaking circuit+ prevent fires. AC
neutral wire= blue on left. Takes electron away from device. DC
earth wire= protect from electrocution, attached from casing to prevent being live.
device covered in plastic doesnt need earth wire, and double insulated.

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Most atoms are stable, some too heavy or light release radioactivity to become stable.
called decay, number of decay per second=activity, measured in Becquerels (Bq).
radioactive particles=invisible, only detect by sensing the ionisation.
ionisation when electron is lost or gained from atom leaving it charged.
Photofil, geiger counter or cloud chamber detect ionisation of radioactive particles
ionisation in human can cause mutation of DNA and over long period can cause cancer or death.
most element have isotopes, same number of protons or electrons but different number of nuetrons, different masses.
3 different radiation radioisotope gives out, alpha- helium nucleus(2proton, 2nutron) mass of 4 and charge of 2+, most ionising easiest to stop, stopped by paper.
beta- fast moving electron, mass of 1/1600, negitive charge, stopped by thick aluminium.
gamma- high frequency EM wave, least ionising, most penetrating, reduced by lead or concrete.
radioactivity given out naturally by air, rocks and cosmic rays, background radiation.

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decay causes origanal atom to change, over time amount of radioactivite atoms go down and therefore activity
the time it takes the activity or the number of original atoms to half= half life, consistant for particular radioisotope.
used in carbon dating, only living absorb carbon dioxide from air during their lives, when dead isotope called carbon-14 decays, carbon-12 doesn't. Compare the ratios work out the age. do same with rocks but with uranium, longer half-life.

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Human use sources, radioactive liquids or solids containing radioisotope.
tracer, gamma emitting source added to water in pipe. workers can walk down road above the pipe. when count goes up, leak when goes down, blockage.
tracers used in medicine, radiation added to blood, gamma camera take picture of blood flow, nurse doing it= radiographer. use gamma, needs to penetrate body to be detected, low half-life so count is high and leaves body quickly.
Gamma used in radiotherapy, firing gamma rays through brain damages cells, worth risk so no cutting head open.
reduce risk by using 3 rays focussed on single point, rotated around the head. apart from focus point, cell can repair and damage not perminant.
gamma rays used to sterilise needles and food like strawberries, sealed before bacteria killed, gamma through container.
Alpha used in smoke alarm, ionised air between positive and negitive terminal, allows current to flow. smoke enters the alarm absorbs alpha particles, preventing ionisation, preventing current flow, alarm will sound.

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use nuclear fission, slow moving neutron absorbed by nucleus of uranium-235, split into two smaller atoms, releasing energy, 2 or 3 fast moving nuetrons.
two smaller particles are radioactive, need disposal, bury low level waste in loandfill but high waste needs to be incased in glass and buried deep underground.
fast moving neutrons go onto further splits, chain reaction. Nuclear bomb just enough uranium that natural collisions between atoms slow them down enough.
Nuclear power station graphite moderator is used to slow them down quicker.
bomb unconrolled and nuclear power station controlled. nuclear power station we used boron control rods. lowered into reactor and absorb neutrons preventing further splits.
Modern nuclear bomb now use fusion, 2 hydrogen atoms combind releasing energy, fusion happens naturally by sun but we cant control huge amount f energy released.
fusion needs very high temp to start it, two scientists Fleishmann and Pons claimed to have done cold fusion, at room temp but not verification so not accepted.

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