gcse science physics unit P4

  • Created by: charlie
  • Created on: 14-06-13 12:13

static electricity

build up is caused by friction 

  • two insulators rubbed e- scraped off one + dumped onto other- leaving +ve + -ve charges 
  • -ve + +ve charged objects attract to neutral objects nearby 
  • which way e- transferred depends on objects involved 
  • e.g polythene rod- e- from duster to rod + acetate rod e- from rod to duster 

only the elctrons move- flow down to ground if -ve charge + up strap if +ve charge 

when static electricity is a nuiance: 

  • attracting dust (+ve charge)- attracted to anything opposite many thing are insulators (TV)
  • synthetic clothes- when dragged over head leave with static charges- cling + leave sparks/ shocks as charge rearrange 
  • door handle shocks- nylon carpet- insulating soles- charge builds on body- metal door handel charge flows 

dangerous-charge builds up on synthetic clothes or fuel flowing out of filler pipe or paper drags over rollers or grains shoot out of pipe enough so create a spark- corrected by earthing :

connected to ground using conductor - easy route- no charge builds up- use antistatic sprays + liquids making surface of charged object conductive - anti-static clothes are conductive - or use insulating mats + soles on shoes 

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uses of static electricity

paint sprayers to get an even coat 

  • spray gun charged- charging up all drops of paint- each drop repels each other giving fine spray
  • object given oppposite charge  to gun- attracting fine paint sprays 
  • method gives even coat, hardly any wasted paint, no paint shadows (parts pointing away)

dust precipitators clean up emissions 

  • wire grid with high voltage + -ve charge so dust particles gain e- + become -ve charge 
  • dust particles induce charge on earth metal plates- -ve charge dust particles repel e- on plate
  • dust particles attracted to metal plates- stick + become heavy- fall + removed from chimney

defibrillators in restarting a heart 

  • shock stopped heart back into operation using tow paddles + power supply 
  • placed on chest to get good electrical contact 
  •  everyone moves away except operator who is holding insulated handles 
  • charge passes to the patient causing heart to contract 
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charge in circuits

  • current= flow of electrons around a circuit - relies on voltage across component to flow through
  • voltage= driving force pushing current- 'electrical pressure' 
  • resistance= something slowing flow of current 
  • increase voltage- more current flows 
  • increase resistance- less current flows or more voltage needed to keep same current flowing 
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plugs + fuses


  • LIVE WIRE = carries voltage alternating between high +ve and -ve voltage around 230v 
  • NEUTAL WIRE = completes circuit in through live + out through neutral always 0v
  • EARTH WIRE + fuse = for safety + work together 
  • appliances with metal cases must be earthed- reduce danger of elctrical shocks 
  • double insulated appliance- casing thats non-conductive 

earthing + fuses prevents fires+shocks 

  • fault in live wire- touching metal case- instantly big current through live wire+ out via earth wire
  • current blows fuse causing wire inside to melt- cuts off live supply- breaking circuit 
  • isolates whole application making it impossible to get an electric shock 
  • prevents flex overheating + causing fire + prevents damage to appliance 
  • circuit breaker is fuse which trips + can be reset 
  • fuses rated just above normal operating current - so not too high that they wouldnt blow 

power = voltage x current 

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variable resistors 

  • alternating current flow through a circuit - move slider length of wire with current changes 
  • longer wires have more resistance - more material has to flow through 
  • thinner wires have more resistance - less space for electrical charge to flow through 

resistance = voltage / current (on front of booklet)

  • ammeter measures current in amps- placed in series (in line) with other components 
  • voltmeter measures voltage in volts- placed in parallel around component being tested 
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ultrasound treatments + scans

sound is longitudinal wave

  • make compressions + rarefractions in arrangments of particles for materials travelled through 
  • compressions (high pressure) lots of particles- rarefractions (low pressure) fewer particles 
  • WAVELENGTH = full cycle of wave compression to compression 
  • FREQUENCY = how many complete waves passing certain point each second (Hertz)
  • AMPLITUDE = how much energy wave is carrying or how loud sound is - measured on oscilloscope in transverse waves from middle line to crest 
  • LONGITUDINAL WAVE= vibrations travelling in same direction as wave 
  • TRANSVERSE WAVE= vibrations at 90d to direction of travel of the wave 

ultrasound is higher frequency than we can hear 

  • produced by electrical device producing elecrtical oscillations of longitudinal waves above human hearing
  • uses : 
  • breaking down accumulations (kidney stones)- high energy waves breaking into small sand particles that cen be esily passed in urine - non invasive + painless
  • body scanning- boundary between 2 diff. media- some reflected back + detected at diff times as depth varies- echoes create image  - due to exact timing + distribution
  • X-rays can only produce images of hard things + produce ionising radiation damaging living cells 
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radioactive decay

radioactivity comes from unstable nucleus 

  • unstable nuclei decay naturally at random give out radiation of alpha, beta + gamma 
  • gamma radiation happens after A + B emission + neucleus has extra energy to lose 
  • gamma so light that doesnt affect atomic mass
  • isotopes are atoms with same atomic number but diff. atomic mass 

alpha radiation has helium nucleus (2 protons + 2 neutrons charge of +2)

  • when emitted mass no. decreases by 4 + atomic no. by 2 forming new isotope
  • nuclear equation e.g: 

beta radiation is fast moving electon  (no mass + charge of -1)

  • mass no. doesnt change + atomic no. increases by 1 forming new isotope 
  • neuclear equation e.g:
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radioactivity + half-life

radioactivity decreases over time 

  • unstable neclei decay radioactivity of source as a whole decreases- older- less radiation emits
  • hard to measure how quickly radioactivity decreases as never reaches zero, so use half-life: 
  • - half-life is the time takens for half of the radioactive nuclei now present to decay 
  • short half-life means activity falls quickly- lots of nuclei decay in short time 
  • long half-life means activity falls more slowly- most of nuclei dont decay for a long time 

half life questions:

  • activity of radioactive sample is 640 Bq. two hours later it has fallen to 40 Bq, find its half life? 
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ionising radiation

harms living cells 

  • A, B, G + X-rays are all ionising radiation- enter living cells- interact with molecules- producing ions 
  • X-rays + gamma rays transfer energy to e- who have enough energy to escape leaving +ve ion
  • Beta remove e- from atoms collided with making +ve + stick to atom making -ve ion
  • Alpha remove e- from atoms passed or hit making +ve 
  • Alpha good ionisers- large for easy collisions + highly charged so easily remove e- 
  • lower dosage of ionising radiation minor damage without killing- lead to rise in mutant cells who divide out of control forming cancer
  • higher dosage kills cells completely - radiation sickness 

dangerous  - 

  • outside body- B + G as they can still get inside to delicate organs 
  • inside body- A as damage very localised + stays inside as cant pass through the skin 

X-rays + gamma rays are electromagnetic waves- high frequency, short wavelenghth

  • gamma rays- from unstable atomic nuclei when decaying 
  • X-rays- firing high speed e- at heavy metal(tungsten)+easier to control- varying amounts absorbed produce image
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medical uses of radiation

radiotherapy- treating cancer using gamma rays 

  • directed carefully at cancer + at right dosage to not kill too many normal cells 
  • fair bit of damage to normal cells makes patient feel ill but kills cancer 
  • 1) gamma rays focussed of tumour using wide beams 2) beam rotated round patient with tumour at centre 3) minimises exposure to normal cells- reducing damage to body 

tracers in medicine- using short half-life gamme + beta emitters 

  • short half-life allows it to quickly disappear 
  • progress followed via radiation detector 
  • e.g. iodine-123 absorbed by thyroid gland- gives out radiation as to whether thyroid gland is absorbing the iodine like it should 

sterlising surgical equipment using gamma rays 

  • kills all microbes 
  • doesnt involve boiling so heat senstive euqipment (thermometers, plastics) arent damaged 
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uses of radiation + background radiation

tracers in industry to find leaks 

  • squirt gamma emitting isotope + go along detecting until reduction or stops- must be leak 
  • gamma so can travel through metal + earth - good as no need to dig up the road 
  • short half-life so isnt hazardous + collected elsewhere 

smoke detectors use alha radiation 

  • weak alpha source in detector between two elctrodes- ionsing air particles- allows current flow
  • smoke particles from fire hit by alpha particles instead 
  • causing less ionisation + current reduced making alarm sound 

background radiaiton comes from many sources 

  • all around us: air, food, building materials, natura sources 
  • radiation from space- cosmic rays- mostly from sun 
  • human acitivities- waste from industries + hospitals 
  • amount of background radiation you are exposed to depends on where you are + your job 
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radioactive dating

  • by measuring amount of radioactive isotope left in sample + know half-life  you can work out age 

radiocarbon dating- carbon-14 calculations 

  • carbon-14 makes up one ten-millionth of carbon in air- stays fairly constant in atmosphere 
  • same propotion found in living things
  • dies + stops exchanging gases so carbon-14 trapped inside- half-life of 5730 years 
  • e.g. axe handle contains 1/40,000,000 carbon-14, how old is it? 

dating rocks- relative proportions

  • uranium isotopes have very long halve lifes + decay via series of short lived particles producing stable isotopes of lead 
  • relative proportions of uranium to lead can be used to calculate age 
  • half life of uranium-238 = 4.5 billion years 
  • (uranium: lead)         intially - 1:0        one half life - 1:1        two half lives - 1:3 
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nuclear power

nuclear fission- splitting up of uranium atoms 

  • controlled chain reaction of uranium/plutonium splits to release energy in form of heat 
  • heat- heats water - producing steam - turns turbine - drives generator - producing electricity 

splitting up urnaium-235 needs neutrons 

  • stable- so needs to be made unstable to split by absorbing slow neutrons which are fired at it 
  • joing to creat U-236 splitting into smaller nuclei- loads of energy + radioactive waste 
  • releases 2-3 fast-moving neutrons which go on to produce cahin reaction 

nuclear bombs are uncontrolled chain reactions 

contol rods are used in nuclear power to contol the chain reaction: 

  • free neutrons kick start fission process 
  • neutrons collide with uranium causing them to split + temp rises 
  • control rods (often boron) limit fission rate by absorbing extra neutrons 
  • stops reaction going out of control but allows some to keep chain reaction going 
  • gas-cooled nuclear reactor uses CO2 to take heat away so it can be used to make steam 
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nuclear fusion

joing of small atomic nuclei 

  • two light nuclei combine to create larger nucleus 
  • 1H1 + 2H1 = 3He2 
  • for given mass it releases a lot more energy, happens in stars under high temps + pressures
  • few experiments happening now (JET)- none produing elecrticity- more energy in that out 
  • carried out by groups to share the costs, expertise, experience, benefits 
  • fusion bombs or H bombs- fission to create really high temps then fusion  

postives + negatives 

  • doesnt leave behind much radioactive waste + plenty to use as fuel 
  • needs really high temps (10,000,000d.c) + pressures that no material can physically withstand
  • hard to saftey control 

cold fusions- nuclear fusion at room temp - stated that it had been acheived in 1989 + experiments + data were shared with other scientists to try but few managed to reproduce reliably

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