what is the build up of static caused by?
friction
negatively charged electrons are...
scraped off one and dumped on the other
what do electrically charged objects attract?
small objects
polythene
duster to rod
acetate
rod to duster
nuclear fusion
joining of small atomic nuclei
does fusion release more energy than fission?
yes
big problem with fusion
really high temperatures
what would you need
extremely strong magnetic field
at the moment
takes more power to get temp up than reactor can produce
define nuclear fission
the splitting up of atomic nuclei
nuclear power stations generate electricity using...
nuclear reactors
what happens in a nuclear reactor? (chain reaction)
atomic nuclei split up and release heat energy
for nuclear fusion to happen...
a slow moving neutron must be absorbed
the addition of a neutron makes the nucleus...
unstable
what happens each time a nucleus splits?
2 or 3 neutrons are spat out
why are the new nuclei radioactive?
wrong amount of neutrons
nuclear fission gives out...
lots of energy
why are the nuclei usually radioactive?
wrong number of neutrons
what does nuclear fission give out?
lots of energy
why are nuclear bombs more powerful than other bombs?
give out more energy
main problem with nuclear power
waste
nuclear power stations generate electricity using
nuclear reactors
what happens in a nuclear reactor
controlled chain reaction takes place where atomic nuclei split up and release energy
what must happen for nuclear fission to occur?
slow moving neutron absorbed
food and medical instruments
high does of gamma rays kill microbes
advantage of irradiation
high temperatures
is the food radioactive afterwards?
no
the isotope used needs to be a
strong emitter of gamma rays with a reasonably long half life
what do smoke detectors use?
alpha
how do smoke detectors work?
weak source of alpha placed in the detector close to 2 electrodes, the source causes ionisation and a current flows, if there's a fire the smoke will absorb the radiation
what can be injected into people?
radioactive isotopes, progress is tracked around the body using an external detector
example of tracers in medicine
iodine-231
what is iodine-231 absorbed by?
thyroid gland, gives out radiation so it can be indicated whether the thyroid gland is taking in iodine
why must isotopes taking in the body be gamma or beta?
passes out of the body
naturally occurring unstable istopes
air, food, building materials, rocks
space
cosmic rays (sun)
man made resources
nuclear weapons tests, nuclear accidents, dumped nuclear waste
underground rocks cause...
higher levels at the surface, especially if they release radioactive radon gas
who are exposed to 10x the normal amount of radiation?
nuclear industry workers, uranium miners
where does background radiation increase?
high altitudes
democritus
all matter made up of identical atoms
dalton
different atoms
jj thomson
discovered electrons could be removed from atoms
plum pudding theory
spheres of positive charge with negative charges stuck in them
what did rutherford and marsden do?
fire a beam of alpha particles at thin gold foil
what did r and m expect?
alpha particles would be slightly deflected
what actually happened?
most particles went straight through but the odd one came straight back
what 3 things did rutherford and marsden realise?
1) most of the mass concentrated at the centre of a tiny nucleus 2) positively charged 3) most of an atom is empty space
why does the atom have to be positively charged?
repelled the alpha particle which has positive charge
what happens if the live wire touches the metal case?
too great a current flows through live wire, through the case and out down the earth wire
what does the surge do?
melt the fuse, cuts off the live supply and breaks the circuit
what does breaking the circuit do?
isolates appliance
fuse ratings increase with
cable thickness
earthing means
attached to an earth wire
what can an earthed conductor never become?
live
double insulated
plastic casing, no metal parts showing
how can circuit breakers be reset?
flicking a switch
what do rccbs detect
small changes in current
rccbs break the circuit as soon as there is a
current surge
what do rccbs work for?
small current changes
what could small current changes end up being?
fatal
wires
correct pin, firmly screwed in, no bare
cable grip
fastened tightly over outer layer
thicker cable means...so...
less resistance, carries more current
metal parts
copper
cable, cable grip and insulators
rubber/plastic
live wire
alternates between high +VE and low -VE voltage
neutral wire
always at 0v
what do 2 wires does the electricity flow in through?
live and neutral
earth wire
protects wiring and safety
what is the earth wire attached to?
metal casing
what does the earth wire do?
carries electricity to the earth
what's a diode?
special device made out of semiconductor material
what is a diode used to do?
regulate potential difference
what do leds indicate
presence of current
what are leds used in?
tvs, digital clocks, traffic lights, remote controls
ldr, in bright light...
resistance falls
ldr, darknesss...
high resistance
what are ldrs used in?
automatic night lights, burglar detectors
thermistor, in hot conditions...
resistance drops
thermistor, in cool conditions...
resistance goes up
what are thermistors useful in?
thermostats
what happens when an electrical charge flows through a resistor?
electrical energy is transferred to heat energy
what does heat energy cause?
ions to vibrate more
how do regenerative brakes slow down the car?
put the motor in reverse
what does the motor in a regenerative braking system act as?
electric generator
how do regenerative brakes conserve energy?
kinetic energy is stored as chemical energy
what does cars slowing down very quickly mean?
kinetic energy is transferred in a very short period of time
in a crash there are big changes in...
momentum
big changes in momentum mean
huge forces
what are cars designed to do?
convert kinetic energy in the safest way
how do cars save people?
increase the time over which momentum happens, lessening the force
crumple zones- as the car body changes shape...
kinetic energy is converted
what do crumple zones do?
increase the impact time
what do crumple zones decrease?
force produced by changes in momentum
what are side impact bars?
strong metal tubes in door panels
what do side impact bars do?
direct kinetic energy away from passengers
what do seat belts do?
increase the time the wearer stops
what do seat belts reduce?
forces in the chest
how do seat belts affect kinetic energy?
absorbed by the seat belt stretching