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
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
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
plugs + fuses
plug
- 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
resistance
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
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
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:
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?
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
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
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
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
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
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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