Physics Unit 2

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  • Created by: Kerry
  • Created on: 22-01-13 18:42
Speed
How fast your going, no regard to direction
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Velocity
How fast your going and the direction e.g. 30mph North
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Calculating Speed from a distance - time graph
Vertical gradient / horizontal gradient
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Acceleration (m/s squared)
How quickly velocity is changing, can be speed or direction. Acceleration = change in velocity / time
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Velocity time graph: curved line
Changing acceleration
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Velocity time graph: area under graph
Distance travelled in the time interval
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Gravity
Attracts all masses, gives everything weight, measured in newtons (N)
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Mass, weight and gravity
Weight = mass (kg) x height (m) x gravity
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Resultant force
Overall force on a object, if it is more than zero then there is a change in velocity/acceleration
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Resultant force = 0
A stationary object will remain stationary, moving object will move at same velocity
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Non=zero resultant force
Will always produce acceleration/deceleration
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Resultant force and acceleration
F = ma or a (m/s/s) = F (N) / m (kg)
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Reaction force
A force that acts in the opposite direction to an action force and is equal - no resultant force
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Friction
If an object has no force acting on it forwards it will slow down/stop due to friction, acts in the opposite direction to movement
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Resistance/drag (liquids and gases)
Resistive force like friction, increases as speed increases
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Terminal velocity
Maximum speed an object can reach
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Stopping distance
Distance covered in the time between the driver spotting the hazard and the vehicle coming to a complete stop, increases as speed increases
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Thinking distance
Distance the vehicle travels during drivers reaction time, affected by: speed, tiredness, alcohol, drugs, bad visability and distractions
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Braking distance
Distance the car travels under the braking force, affected by: speed, brake quality, tyre quality, road surface and weather
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Work
When a force moves an object through a distance energy is transferred and work done, measured in joules, work done = force x distance
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Gravitational potential energy
Energy due to height, increases as height increases, Ep = m x g x h (measured in joules
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Kinetic energy
Energy of movement, kinetic energy gained = Ep energy lost, Ek = 1/2 x m x v2
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Elastic potential energy
Work is done to an elastic object to change its shape and this energy is stored as elastic potential energy
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Extension and force
Extention of a stretched spring is directly proportional to force, F = k x e , k is the spring constant - varies depending on the material, measured in N/m
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Maximum elastic force
Theres a limit to the maximum force an object can take and still extend propotionally, known as the limit of proportionality, once past this point the object is permanently stretched
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Power
Is the rate of doing work, power = work done / time taken, measured in watts/joules
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Momentum and collisions
A property of a moving object, greater the mass of an object the greater the velocity therefore the more momnetum it has, momentum = mass x velocity (measured in kg m/s)
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Momentum before = momentum after
Conservation of momentum
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Closed system
When no external forces act
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Force causes change in momentum
Larger force means a bigger increase in momentum, can cause injury - car crash, cars designed to take longer for the change in momentum - smaller force
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Car design and safety
Regenerative brakes put the vehicles motor into reverse, instead of converting heat to kinetic, kinetic - electrical - chemical, store energy instead of wasting it
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Crumple zones
Cars kinetic energy is converted into different forms of energy by car body as it changes shape, increase impact time - decreasing the force produced by change in momentum
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Side impact bars
Metal tubes fitted into car door panels, direct kinetic energy of crash away from passengers to other areas of car - crumple zone
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Seat belts
stretch slightly, increase time for wearer to stop - reduces forces acting on the chest, kinetic energy of wearer is absorbed by seat belt stretching
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Airbags
Slow you down more gradually and stop you from hitting hard surfaces in the car
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Power of a car
More powerful a car the higher its top speed, aerodynamic so less air resistance
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Static
When certain insulating materials are rubbed together -ve electrons move to one of the materials, when 2 objects are brought close together they exert a force on each other - repel or attract
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Examples of static
Polythene rod: electrons move from duster to the rod, acetate rod: electrons move from the rod to the duster
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Current
Flow of electrical charge round the circuit, will only flow through a component if there is potential difference across that component, Unit: ampere (A)
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Potential difference
The driving force that pushes the current around, Unit: volt (V)
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Resistance
Anything in the circuits that slows the flow/current down, Unit:ohm
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Resistance and current
Greater the resistance across a component the smaller the current that flows (for a given p.d across the component)
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Current, charge and time
More charge passes when a bigger current flows, current = charge/time or I = Q/t
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Potential difference formula
Work done per unit of charge, across an electrical component is the amount of energy transferred per coulomb of charge, P.D = work done / charge
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Standard test circuit
Cell, variable resistor, ammeter, component and a voltmeter
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Ammeter
Measures current flowing through the component, placed in series
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Voltmeter
Measures potential difference across a component, placed in parallel around the component under test
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Important points
Test circuit for getting V-I graphs, variable resistor varies the current flowing through a circuit,
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Different resistors V-I graph
Ohmic resitor, current through a resistor at a constant temp is directly proportional to p.d
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Filament lamp V-I graph
Non-ohmic resitor, as voltage increases, temperature of filament increases and resistance increases hence curve
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Diode
Current will only flow in one direction, diode has a very high resistance in the opposite direction
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Resistance and temperature
Heat energy causes ions in conductor to get hot and vibrate more so is more difficult for electrons to get through, current cant flow as easily
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Resistance, current and p.d
Potential difference = current x resistance, steeper the graph the lwoer the resistance, curve means it is changing, can get values for formula from graph
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Diode
Made from a semi conductor - silicon, regulate p.d in circuits, useful in electronic circuits, doesnt let current flow automatically
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LED (light emitting diode)
Emits light when current flows through it in the forward direction, use a smalelr current than other forms of lighting, indicate present of current in circuit, used in traffic lights, digital clocks and remote controls
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LDR (light dependent resistor)
dependent on the intensity of light, in bright light resistance falls, darkness resistance is highest used in automatic night lights, street lamps and burglar detector
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Thermistor
Resistance of a thermistor decreases as temperature increases, temperature dependent resistor, used in electronic thermostats
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Series circuit
Components connected in a line between +ve and -ve power supply, if one is removed circuit is broken
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Series: Potential difference
Total pd of the supply is shared between various components, voltages around circuit add up to total
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Series: Current
Is the same everywhere, size of current is determined by pd and resistance
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Series: Resistance
Adds up, bigger the resistance of a component the bigger its share of pd
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Parallel circuit
Each component is separately connected to the +ve and -ve power supply, if one is removed then others arent affected,
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Parallel: Potential difference
All components get the full source pd so voltage is the same across all components, identical bulbs connected in parallel have same brightness
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Parallel: Current
Total current flowing around circuit is equal to total of all the currents through the seperate components, junctions is where current splits or joins
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Parallel: Resistance
Reciprocals = 1/r = 1/r1 + 1/r2 ... = 1/R = 2/10..
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Mains electricity
approx 230 volts AC, frequency of 50Hz, cells and batteries are DC
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Oscilloscope
Shows voltage, gain dial shows how many volts each cm division represents, timebase dial shows how many millisecs each division represents
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Frequency
1/time peroid (time period is time to complete one cycle)
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Hazards
Long cables, frayed cables, cables in contact with something hot/wet, water near sockets, damaged plugs, overloading of sockets, appliances without their covers one
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Three core cables
Three wires with cores of copper and coloured plastic coating, live wire is brown - alternates between high +ve and -ve voltage, neutral wire is blue - always 0v, earth wire is green/yellow, for protecting the wiring and safety - carries it to earth
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Plug features
Metal parts made of copper/brass - good conductors, case,cable grip and insulation are made of plastic/rubber - good insulators and flexible
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Earth wire and fuse/circuit breaker
Prevent electrical overload, if a fault develops flows down earth wire, surge in current melts fuse/trips - cuts off live supply and breaks the circuit
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Fuses
Should be rated near as possible but just higher than the current, melts when current is greater than fuse rating
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Cables
The larger the current the thicker the cable is - fuse rating increases with cable thickness
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Circuit breakers
Open switch when they detect a surge in current, can be reset easier and not replaced, more expensive than fuses
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Power of appliances
Total energy transferred by a appliance depends on its power rating and time its on for, power is the energy it uses each second Energy transferred = power rating x time
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Electrical power
Power = current x potential difference - used to work out fuse needed as well
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Potential difference and charge
Bigger the charge in voltage then the more energy is transferred for a given amount of current, Energy transformed = charge x potential difference
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Thomsons theory
Plum pudding - atoms are the puddings with electrons the plums stuck in them
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Rutherford and Marsden
Fired an alpha beam at thin gold foil, thought alpha particles would be slightly deflected, most went straight through but some came straight back
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Conclusions
Realised most of the mass was concentrated at center in a tiny nucleus, has +ve charge as repelled alpha particles, showed most of atom was an empty space
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Isotopes
Atoms of the same element with different numbers of neutrons, usually only one or two stable ones per element - unstable ones are radioactive
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Radioactive elements
Decay into other elements and give out radiation
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Sources of background radiation
Naturally occuring - rocks, air, food etc, from space - cosmic rays mostly from the sun, man made sources - nuclear accidents or dumped nuclear waste
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Alpha particles
Helium nuclei, 2n and 2p, big, heavy and slow moving, strongly ionising (crash into atoms and knock electrons off them), dangerous inside the body, weakly penetrating
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Beta particles
Electrons, move quite fast and are quite small, penetrate moderately, long air range, moderately ionsing, for every beta particle emitted a neutron turns to a proton in the nucleus, have no mass and -1 charge
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Gamma rays
Very short wavelength electromagnetic waves, opposite of alpha particles, penetrate far into materials without being stopped and pass straight through air, weakly ionising - do a lot of damage if they hit something, no mass or charge
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Damage caused by radiation
Depends on type and amount of radiation you have been exposed to
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Locations and occupations with high amounts of radiation
Underground rocks - granite, nuclear industry workers, uranium miners, radiographers, pilots, miners
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Electric and magnetic fields
When alpha and beta travel through magnetic/electric field they are deflected in opposite direction because of opposite charge, alpha deflected less because of larger mass, gamma radiation isnt deflected as is EM wave and has no mass or charge
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Half life
Average time it takes for number of nuclei in a radioactive isotope sample to halve, decay is completely random
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Uses of radiation
Smoke detectors - alpha, tracers in medicine - short half life beta or gamma, radiothrapy - gamma, sterilising food/medical equipment - gamma
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Radiation safety precautions
Use sources for short time, never allow skin contact - use tongs, hold source at arms length, lead absorbs all radiation - aprons, boxes etc
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Nuclear fission
Splitting up of large atomic nuclei, controlled chain reaction releases energy in form of heat - used to heat water and produce steam - turns turbines, connected to electricity generator, uranium 235 or plutonium 239
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Nuclear fission
Slow moving neutron is absorbed into pluto/uran nucleus, makes nucleus unstable so it splits, everytime its splits it releases 2 or 3 neutrons that keep chain reaction going, if not controlled can cause and explosion
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DIsadvantages of nuclear power
Products are radioactive, cost of nuclear power is high, radiation leaks
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Nuclear fusion
Joining of small atomic nuclei, releases more energy than fission, doesnt leave radioactive waste, has to happen at to high a temperature, takes more power to produce than can be produced
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Nuclear fusion
Light nuclei eg hydrogen join to create a larger nucleus, energy released in stars comes from fusion
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Protostar
Form from clouds of dust and gas (nebula) , force of gravity makes gas and dust spiral intogether to make a protostar
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Main sequence star
Gravitational energy --> heat energy so temp rises, hydrogen nuclei undergo nuclear fusion to form helium nuclei and give out huge amounts of heat and light, smaller masses of gas and dust may make planets that orbit stars
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Long stable period
Star immediately enters logn stable period where heat created from nuclear fusion provides outward pressure thats balanced by force of gravity pulling it inwards, maintains energy output due to lots of hydrogen
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Planetary nebula
Small to medium sized stars become unstable and eject their outer layer of dust and gas as a planteray nebula
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White dwarf
This leaves behind a hot, solid, dense core, no nuclear reactions happening as no hydrogen left, cools to black dwarf and disappears
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Red giant/super giant
Hydrogen begins to run out, heavier elements like iron are made by nuclear fusion of helium, star swells into red giant, red super giant if its a big star, red because surface begins to cool
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Supernova
Big stars start to glow brightly as they undergo fusion of helium --> iron, explode into supernova and ejects elements heavier than iron into universe to form new planets and stars
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Neutron star
Exploding supernova throws out outer layers of dust and gas into space - leaves dense core known as neutron star, if star is big enough will become a black hole, mass is very compressed and gravity strong
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Other cards in this set

Card 2

Front

How fast your going and the direction e.g. 30mph North

Back

Velocity

Card 3

Front

Vertical gradient / horizontal gradient

Back

Preview of the back of card 3

Card 4

Front

How quickly velocity is changing, can be speed or direction. Acceleration = change in velocity / time

Back

Preview of the back of card 4

Card 5

Front

Changing acceleration

Back

Preview of the back of card 5
View more cards

Comments

Crystal Blue ♥

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Great but there are too many :( Would be helpful if they were a bit more condensed

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