# Physics P2

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• Created by: wafflypig
• Created on: 12-03-16 14:45
3 methods of car safety?
Seat belts, airbags and crumple zones
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Moderately ionising, quite fast, -1 charge, small mass, ejected electron, stopped by aluminium
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Weakly ionising, very fast, no charge, no mass, EM wave, stopped by a few inches of lead
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Highly ionising, very slow, 2 protons and 2 neutrons (He), heavy mass, stopped by skin or paper
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Smoke alarms, when current stops, alarm sounds.
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Medical tracers, thickness control
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Treat cancer, sterilising medical equipment and food
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Things that effect braking distance?
Speed, mass, quality of brakes, weather conditions (aquaplaning), grip
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Things that effect thinking distance?
Speed, reaction time (drugs, tiredness etc.)
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Define current?
The rate of flow of charge, measured in Amps (A)
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Define work done?
Work is done when energy is transferred by a force moving an object
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Define power?
The rate of energy transfer
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How can a build up of static charge cause an explosion in a petrol tank?
The electrons are transferred to the insulator and held there, this build up may lead to a spark, light the fuel and cause an explosion
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What is earthing?
Earthing provides a self route for excess electrons to reach the ground through a conductor (usually copper wire).
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What is potential difference?
PD is the difference of electrical potential between two points in a circuits.
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What is voltage?
The driving force of the current in the circuit
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What is Ohm's Law?
Current and voltage are directly proportional; current and resistance are inversely proportional
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What is Newton's 2nd Law?
Unbalanced forces acting on an object, results in a resultant force meaning there will be an acceleration. A greater resultant force = greater acceleration
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What is Newton's 1st Law?
When forced acting on an object are balanced, the object will stay at rest or continue at the same velocity
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What is Newton's 3rd Law?
Equal and opposite forces. When body A exerts a force on body B, B will exert an equal but opposite force on body A
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How can charge build in a thundercloud?
Chunks of ice knock into each other, building up an electrostatic charge, resulting in a lighting strike
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Uranium is abundant and cheap, it is reliable, safer than people think, doesn't burn fossil fuels
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The waste has a long half life (dangerous for a long time), risk of leaks, overall cost is high
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What is nuclear fusion?
The joining together of two light nuclei to form a larger nucleus, releasing energy. E.g. two hydrogen = helium
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Describe the process of nuclear fusion...
It must happen at very high temperatures and pressures, must be in a magnetic field because anything else would melt.
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Not much waste
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What is nuclear fission?
The splitting of a large nucleus by firing a neutron at it to form two, smaller daughter nuclei
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Describe how uncontrolled fission can lead to a runaway reaction?
There will be lots more neutrons so split up more and more uranium atoms which go on to split more and more, releasing more and more energy, could result in nuclear meltdown
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How can a fission reaction be controlled?
Moderators slow down the speed of the free neutrons so they are slow enough to be captured by the uranium nuclei. Control rods (graphite/boron) are lowered as needed to absorb excess neutrons to stop a runaway reaction
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Use of nuclear fusion?
In stars
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Use of nuclear fission?
To power nuclear power stations
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How is terminal velocity reached?
When an object falls forces acting on it gradually become more balanced. Eventually, weight will equal air resistance so there will be no acceleration. It will travel at a constant velocity.
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Define acceleration?
The rate of change of velocity
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What can the are under a V-T graph be used to calculate?
Distance
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What is a negative gradient on a D-T graph?
Returning to start point
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What is a curve on a D-T graph?
Acceleration
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What does flat mean on a D-T graph?
Stationary
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What does a curve mean on a V-T graph?
Changing velocity
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What is a flat line on a V-T graph?
Constant velocity
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What is the relative mass of an electron?
1/1860
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What are the dangers of alpha radiation to humans outside the body?
None
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Dangers of beta and gamma radiation?
Can penetrate skin and has potential to turn body cells cancerous or even kill them
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How is aircraft adapted to cope with a build up of electrostatic charge?
Have black rods to expel excess electrons on back on wings (charge built up against air particles in flight). The have places for earthing wires to be connected under the wings and have insulating tires.
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What is induction?
When charges on an object (e.g. wall) separate depending on the charge of the object being held near it
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How does a balloon get attracted to a wall?
An induction happens
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What are the 4 uses of static electricty?
Electrostatic dust precipitators, laser printers, photocopiers and defibrillators
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What happens at junctions in a parallel circuit?
Current is conserved
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Conservation of energy says that...
Energy can never be created, nor destroyed. It is useful when it is being transferred
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Kinetic energy gained =
Gravitational potential energy lost
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Gravitational potential energy depends on...
Height
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Kinetic energy depends on...
Mass and velocity
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What is the unit for acceleration?
m/s^2
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How is the gravitational field strength on earth?
10 N/Kg
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What is the unit for momentum?
Kgm/s
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What is the unit for work?
Joule (J)
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What is the unit for power?
Watts (W)
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What is the unit for half life?
Bq
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How can half life be shown on a graph?
Using a decay curve
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How can the dangers of working with radioactive materials be reduced?
Hold the course at arms length, thick glass, lead-lined apron, robotic arms
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How can radioactive waste be safely disposed of?
Vitrification, then put deep underground. Or, put in a thick metal container and bury deep under cement
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The top of a thundercloud has which charge?
Positive
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How can you get a shock from your car?
A charge builds between clothes and synthetic car seat when friction happens. Then touch the metal car door and current flows = zap
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How can shocks from cars be prevented?
Have a conducting ***** hanging down from the back of the car for earthing
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What is a DC?
A direct current. Current flows in one direction
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What type of current do mains sockets provide?
Alternating current
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How does an electrostatic paint sprayer work?
The paint gets a negative charge as it moved through the -ve charged nozzle so they are attracted to the +ve charged object
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What are the advantages of using an electrostatic paint sprayer?
Droplets repel each other = even coat and no drips, attracted to all over the object, no waste, no paint shadows
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How can an explosion be the result of a static charge?
Huge charge build - spark - ignites fuel fumes in the air = explosion
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What does earthing do?
Stops the build up of static charge
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Why are metals good conductors?
They have delocalised electrons to carry charge
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Why does a voltmeter need need a huge resistance?
To stop the flow of current through it so it can get a true reading of the PD
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What can be used to measure current?
Ammeter
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Does an ammeter have to be connected in series or parallel?
Either
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True or false, a voltmeter must be connected in parallel?
True
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What does the cell in the circuit supply?
A push force of the electrons in the circuit
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Why do electrons move when a cell is connected?
The positive terminal pushes electrons away (around the circuit) and then the negative terminal gives the electrons energy to get through the negative end of the terminal to go around again
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What is a coulomb?
The unit of electrical charge, 1 coulomb = 1.2*10^18 electrons
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What does the V-I graph of a fixed resistor look like?
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What does the V-I graph of a lamp look like?
An S
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What does the V-I graph of a diode look like?
Exponential function
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What is the unit of resistance?
Ohms (Omega)
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Potential difference is technically...
The energy transferred per unit of charge passed
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True or false, potential difference decreases over a resistor?
True
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What happens in a resistor?
Charges release their energy
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Why must an ammeter have a low resistance?
To not change the current (the thing it's measuring)
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At a junction, the total current leaving is equal to...
the total current entering the junction
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What is a LDR
Light Dependent Resistor
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In bright light, what is the resistance of a LDR?
Low
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What is a thermistor?
Temperature dependent resistor
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In hot conditions, what is the resistance like in a thermistor?
Low
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Why do resistors get hot when a current passes through them?
There is an energy transfer which heats the resistor. The electrons collide with the ions in the lattice which releases energy as heat
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What does a fuse do?
Melt and break the circuit if the current gets too high
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Electrical power is...
The rate at which an appliance transfers energy
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A high power rating means...
Lots of energy is transferred in a short amount of time which draws more current from the supply
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Give an example of a scalar quantity
Speed, time, mass
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What is a vector quantity?
A measurement that has size and direction
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What is displacement?
The distance between two points, regardless of distance travelled
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Speed =
Distance/Time
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Define acceleration
The rate of change of velocity
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A resultant force can be shown using a what length arrow?
Longer
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Force =
Mass * Acceleration
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Braking distance + thinking distance =
Stopping distance
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What is the unit for momentum?
Kg m/s
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Initial K.E. = (in movement)
Work done by breaks to stop vehicle
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True or false, energy transfers involve no losses?
False. Most transfers involve some losses, usually as heat or sound
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Define isotope
Different forms of the same element with the same number of protons but different number of neutrons
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What kind of process is radioactive decay?
Random and spontaneous
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Is the mass number on the top or bottom?
Top
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Is the atomic number on the bottom or top?
Bottom
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How does an alpha particle cause ionisation?
It has a strong charge of +2 so it can PULL electrons out of orbit
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How does beta radiation cause ionisation?
It has a negative charge of -1. There is a force of repulsion between the electrons so they PUSH it out
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How do gamma rays cause ionisation?
It gives electrons energy to break free and become delocalised
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What kind nucleus is an alpha particle?
Helium (He)
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Few cm of aluminium
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How can fission generate electricity?
It released lots of KE (so also heat) which heats water in the boiler which generates steam which turns a turbine which turns the generator
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What do moderators in the reactor do?
Slow the neutrons down so they can be absorbed by the uranium nuclei
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What are control rods often made of?
Boron or graphite
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How can a chain reaction happen in fission?
Each time a uranium nucleus splits, it spits out 2 or 3 neutrons which go on to split other uranium nuclei
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Why does nuclear fusion have to happen at high temperatures?
To overcome the strong forces of electrostatic repulsion
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Which produces more energy, fusion or fission?
Nuclear fusion
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Why has the theory of cold fusion not been fully accepted yet?
MIT discredited the theory, hadn't been peer reviewed and not many other scientists can get the same results
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Who were the two scientists that started the cold fusion theory?
Pons and Fleischmann
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51% (biggest)
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Which factor accounts for less than 1% of the background radiation?
Nuclear industry
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What % of the background radiation comes from cosmic rays?
10%
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Which factors effecting background radiation levels are at 12%?
Medical and food
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What are the factors effecting background radiation levels?
Radon gas, naturally occurring isotopes (rocks), medical, food, cosmic rays, nuclear industry
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Define half life
The time it takes for half the undecayed nuclei to decay
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A short half life means activity falls...
Quickly
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Why do we have to use half lives?
The activity never reaches 0
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What can be used to measure half life?
G-M tube
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The severity of effects from radiation exposure depends on 2 things. What are they?
How much exposure. The energy (some are more penetrative than others)
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Give 3 reasons nuclear waste is a massive problem in the UK?
Nuclear waste can't usually be recycled. Has a really long half life. Really dangerous
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What are the advantages of nuclear power?
Doesn't burn fossil fuels. Uranium is cheap because it's abundant. Safer than people think
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What are the cons of nuclear power?
Risk of leaks. Decommissioning of plants takes decades. People worry waste can never be properly and safely disposed of
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Moderately ionising, quite fast, -1 charge, small mass, ejected electron, stopped by aluminium