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AQA - GCSE Physics Revision

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1 AQA - GCSE Physics Revision
Additional Physics (P2)

2 Chapter 1 - Motion What you need to know: Distance-time Graphs
Finding out when an object is stationary Finding out when an object is moving at a constant speed Velocity and Acceleration The difference between speed and velocity What acceleration is and its units What is deceleration Velocity-time Graphs Finding out if an object is accelerating or decelerating What the area under a velocity-time graph represents Using Graphs Calculating speed from a distance-time graph How we can calculate distance from a velocity-time graph Calculating acceleration from velocity-time graphs

3 Distance-Time Graphs A Constant Speed: An object moving at the same speed travels the same distance every second Speed on a distance time graph is represented by the slope Speed 1 = fast moving object (steep line) Speed 2 = steady moving object (straight sloped line) Speed 3 = stationary object (horizontal line)

4 Velocity and Acceleration
Velocity: speed in a given direction (2 objects can have the same speed but a different velocity due to the direction they are travelling in) Acceleration: the rate at which the velocity of an object is increasing An object travelling at a steady speed is accelerating if its velocity is changing Deceleration = the velocity decreases (negative acceleration) and the object slows down

5 Velocity-Time Graphs Distance Travelled = area under velocity-time graph Acceleration and Deceleration = gradient of the lines Finding the area under the graph Break the area under the graph up into sections and work out the area of separate shapes Once you have worked out the area of each shape add them together *If you are only finding out the acceleration or deceleration you only need to work out the gradient of the sloping line (so only one triangle) Deceleration = -distance / time*

6 Summary How fast = Velocity How far = Distance
How quickly the velocity changes = acceleration Object moving at a constant speed = an increased distance Deceleration on a distance time graph

7 Chapter 2 – Speeding up and Slowing Down
What you need to know: Forces Between Objects When two forces interact what can we say about the acting forces What is the unit of force Resultant Forces What is the resultant force What happens when the resultant force is zero and what happens when it is not zero Force and Acceleration How acceleration depends on the size of the resultant force What effect the mass of an object has on acceleration On the Road The resultant force of a vehicle travelling at a constant velocity What the stopping distance of a vehicle depends on and how the stopping distance can be increased Falling Objects What is the difference between mass and weight What is the terminal velocity

8 Forces Between Objects
Forces can: Twist Pull Push Upthrust Weight/Gravity Thrust Friction Forces are measured in Newtons (N) They act in pairs Each force acts in a certain direction When two forces interact with each other they always exert equal and opposite forces on each other

9 Resultant Force Object at the Start Resultant Force
Resultant Force: working out the effect each force has on an object. This force has the same effect as all the forces acting on the object Object at the Start Resultant Force Effect on the Object 1 (glider) At rest Zero Stays at rest 2 (moving a crate) Moving Velocity stays the same 3 (plane) Non-zero in the same direction as the direction of the moving object Accelerates 4 (car breaking) Non-zero in the opposite direction to the direction of the moving object Decelerates

10 Force and Acceleration
Acceleration depends on: The mass of an object The amount of force applied F A M Mass Acceleration Force Resultant Force (N) = Mass (kg) x Acceleration (m/s²) The velocity increases if: The resultant force is in the same direction as the velocity The velocity is positive The velocity decreases if: The resultant force is in the opposite direction as the velocity The velocity is negative

11 Stopping Distance = Thinking Distance + Braking Distance
On the Road Thinking Distance: distance travelled by the vehicle in the time taken for the driver to react Braking Distance: distance the vehicle travels under the breaking force The breaking force needed to stop a moving vehicle depends on: The velocity of the vehicle The mass of the vehicle Stopping Distance = Thinking Distance + Braking Distance Factors affecting the stopping distance are: Tiredness Alcohol and Drugs Adverse Road Conditions A Poorly Maintained Vehicle Affect Thinking Distance Affect Breaking Distance

12 Falling Objects Weight: the force of gravity upon an object (N)
Mass: the quantity of matter in it (kg) The weight of an object: Of mass 1kg = 10 N Of mass 5kg = 50 N The Earths gravitational field strength is 10 N/kg Weight (N) = Mass (kg) x Gravitational Field Strength (N/kg)) If an object falls freely: No other forces act upon it, therefore the resultant force is its weight. A 1kg object would accelerate at a constant acceleration of 10m/s² (force ÷mass) on previous slide If an object falls in fluid: The fluid drags on the object, and the drag force increases with speed The resistance is weight – drag force When the drag force and velocity are equal the object reaches a terminal velocity (the resultant force is 0 so the acceleration is 0)

13 Chapter 3 – Work, Energy and Momentum
What you need to know: Energy and Work What do we mean by ‘work’ in science What is the relationship between work and energy What happens to the work done against frictional forces Kinetic Energy What is kinetic and elastic potential energy How does the kinetic energy of an object depend on its speed How can we calculate kinetic energy Momentum How can we calculate momentum and what is its unit What happens to the total momentum when two objects collide More on Collisions and Explosions Why does momentum have a direction and size When two objects fly apart why is their total momentum 0 Changing Momentum What does a force do to the momentum of an object How can we calculate the change in momentum caused by force

14 Energy and Work Workdone: when an object is moved by force we say that work is done to the object It can also be the energy transferred/change in gravitational potential energy W D F Force Distance Work Done Work Done/Energy Transferred (J) = Force (N) x Distance (M) G H W Weight Height Gravitational Potential Energy Change of Gravitational Potential Energy(J) = Weight (N) x Change in Height (M)

15 Kinetic Energy Elastic Potential Energy: the energy stored in a elastic object when work is done on the object An object is elastic if it regains its shape after being stretched or squashed Examples of this are: Bow and arrow Elastic band Spring Rubber swimming hats Kinetic Energy (J) = ½ [Mass (Kg) x Speed²(m/s)] KE = ½ mv²

16 Momentum Momentum: the ability for an object to keep moving (relating its mass and velocity) in the same direction Mass in motion P V M Mass Velocity Momentum It is difficult to change the direction of movement of an object with a lot of momentum Momentum is conserved whenever objects interact, as long as no external forces act on them What happens when two cars of the same mass collide? If cars have a combined mass of 1000kg Momentum is conserved (stays the same) Velocity of car 1 is halved by impact The momentum of a moving object(Kg m/s) = Mass (Kg) x Velocity (m/s)

17 More on Collisions and Explosions
Momentum has a size and a direction When two objects push each other apart, they move apart with equal and opposite momentum (Momentum of A) = -(Momentum of B) OR (Mass of A x Velocity of A) = -(Mass of B x Velocity of B) As it is travelling in the opposite direction Changing Momentumm The more time an impact takes, the less force is exerted

18 Chapter 4 – Static Electricity
What you need to know: Electrical Charges What happens when insulators are rubber together What is transferred when objects are charged What happens when charges are brought together Charge on the Move Why metals cant be charged by rubbing them How charge is transferred through conducting materials What happens when a charged conductor is connected to earth Why do some objects sometimes produce sparks Uses and Dangers of Static Electricity In what ways is static electricity useful How can static electricity be dangerous How can we get rid of dangerous static electricity

19 Electrical Charges Van de Graaff Generator Charging by Friction
The dome charges up when the generator is switched on. Sparks are produced if the charge becomes to great. Charge builds up in the dome because: The belt rubs against the felt pad (FRICTION) The belt carries the charge onto the insulated metal dome Sparks are produced when the dome can not hold any more charge Charging by Friction Rubbing two insulators together causes them to become charged Friction causes electrons to be transferred from one material to the other If a material: Gains electrons it becomes negatively charged Looses electrons it becomes positively charged A Polythene Rod transfers electrons from the cloth to the rod A Perspex Rod transfers electrons from the rod to the cloth In the exam they will say which insulator carry’s which charge, unless it specifies which type of rod is being used (here you need to know which insulator transfers electrons)

20 Electrical Current: the rate of the flow of charge
Charge on the Move Electrical Current: the rate of the flow of charge Conductors can only be charged if they: Off of the ground Insulators can only be charged if they: Brought into contact with a charged object Discharging an Object To discharge an object you have to provide a path between the conductor and the ground The path between the object and the ground allows the electrons to flow to the ground – this object is then Earthed (Shown in the diagram below) If it is not insulated from the ground, it wont hold charge as electrons transfer between the conductor and the ground Sparks and Strikes If a metal object (conductor) gains to much charge it will produce a spark between the conductor and the charged object This is because the voltage between the conductor and the ground increase Lighting is an example of this

21 Uses and Dangers of Static Electricity
Uses of Static Electricity Dangers of Static Electricity Paint Sprayer: The paint droplets are given positive charge The car is given a negative charge The droplet and car attract each other The paint droplets repel each other Transporting Oil: If the pipe is not earthed, a build up of charge could cause a spark If there is a spark, an explosion could occur Photocopier: Drum is positively charged until light falls on it Charge is lost in the area where light hits it Black toner sticks to the drum where there is still charge Paper is heated to stick the toner to it Antistatic Floors (in hospitals): Some anaesthetics used in operating theatres are explosive A spark could cause a explosion if any gas has escaped Antistatic material is used on the floor to act as insulator (conducting charge to earth) Electrostatic Precipitator:

22 Chapter 5 – Current Electricity
What you need to know: Electric Circuits What are the circuit symbols for common components Resistance The placement of ammeters and voltmeters Resistance and its unit ‘Ohm’s’ Law Reversing the current in a resistor Current-Potential Difference Graphs When the temperature changes what happens to the resistance in a filament lamp and thermistor How does the current in a diode depend on the potential difference across it When the light level increases what happens to the resistance of a LDR Series and Parallel Circuits The current and potential difference of components in a series circuit and parallel circuit Why cells are connected in series Finding the total resistance of a series circuit and parallel circuit

23 Electric Circuits-Symbols
A component diagram shows how the components in a circuit are connected together Every component has its own symbol. The ones on this slide and the next are the ones you need for GCSE


25 Resistance Resistance (ohms) = Potential difference (volts) Current (amperes) Ammeter: connected in series with the lamp to measure the current going through the lamp Voltmeter: connected in parallel to measure the potential difference across the lamp The current through a resistor of a constant temperature is directly proportional to the potential difference across the resistor

26 Current-Potential Difference Graphs
Thermistor: does no obey Ohm’s Law (is not a straight line) and a reverse of the filament lamp. More current = steeper graph, more heat = more free electrons to carry the current = increased current = reduced resistance Filament Lamp: does not obey Ohm’s Law (it is not a straight line) more current = hotter = atoms vibrate faster increasing collisions with electrons = increased resistance (shown by the flattening out of the graph) LDR: semi conductor. Increase in light = more electrons carrying current = increasing current = reduced resistance, little light = less electrons carrying current = reducing current = increased resistance Diode: does not obey Ohm’s Law (is not a straight line) connected in a forward direction = low resistance, connected in the reverse direction = high resistance

27 potential difference/ the voltage of each cell
Series Circuit The current is the same through all components in series with each other The total potential difference/ the voltage supply in a series circuit is shared between the components The total potential difference/ the voltage supply of the cells is the sum of the potential difference/ the voltage of each cell The total resistance and the components in series is the sum of their separate resistances

28 Parallel Circuit The total current through the whole circuit is the sum of the currents through the separate components For components in parallel, the potential difference/ the voltage across each component is the same The bigger the resistance of a component the smaller the current

29 Chapter 6 – Mains Electricity
What you need to know: Alternating Current What direct and alternating current is Frequency of the UK mains supply Using an oscilloscope Cables and Plugs The casing of a mains plug The colour of the different wires in a plug Which wire is connected to different pins in a plug Fuses What are fuses and circuit breakers used for Why do we have to use a fuse with the correct rating Why appliances in plastic cases don’t need to be earthed Electrical Power and Potential Difference How to calculate the power of an appliance using energy and time How we can calculate electrical power and its units Finding the total resistance of a series circuit and parallel circuit Electrical Energy and Charge (Higher) What is electrical current and its charge What energy transformations take place when charge flows through a resistor

30 Alternating Current (a.c)
Alternating Current: a current which repeatedly reverses in direction You can measure the alternating potential difference using an oscilloscope You can also see the peak potential difference as well as the frequency of an alternating current (Higher) In the UK the frequency of mains electricity is 50 cycles per second (50hz) Mains electricity uses an alternating current In a mains circuit there is a live wire which is alternately positive and negative every cycle and a neutral wire which is always at 0 volts Frequency = 1 Time (sec)

31 Cables and Plugs The pins in a plug are made of brass
Live Wire – is brown and connected to the live pin Neutral– is blue and connected to the neutral pin Earth Wire – is yellow and green and connected to the earth pin (a two core cable does not have a earth wire) which is the longest pin in the plug The pins in a plug are made of brass The cable is copper but is surrounded by an insulator such as rubber/flexible plastic The case of the plug is made out of stiff plastic Earth wires are essential for appliances with metal cases. If the live wire becomes loose and touches the metal case a large current flows to earth, blowing the fuse and breaking the circuit

32 Fuses The fuse sits next to the live wire A fuse is a safety device which breaks the circuit if the current becomes to high It contains a thin wire which melts (breaking the circuit) It is important that you use the correct amp fuse in your appliance. If a larger fuse in used, the fuse will not blow when it is supposed to and the heating effect on the appliance could result in the appliance catching alight Circuit Breakers A circuit breaker is an electromagnetic switch that cuts the current off is the current is too great After being used it can be reset Circuit breakers work faster the fuses and are sometimes fitted into ‘fuse boxes’ to replace fuses

33 Electrical Power and Potential Difference
Power: energy transferred per second The power (watts) is the energy transformed (joules) every second, using the equation below: E T P Power (W) = Energy (J) Time (S) We can also calculate power dissipated (lost) in a device, using the equation below: P V I Power (W) = Current (A) x Voltage (V) Current To make a light bulb shine brighter you can: Increase the voltage (increase the energy delivered) Increase the current (increase the rate at which energy is delivered)

34 Electrical Energy and Charge
Electrical Current: the rate of flow of charge (measured in Coulomb [C]) The charge of an appliance can be calculated using the equation below: C T I Charge Flow (C) = Current (A) x Time (S) Current Resistor is connected to battery Electrons pass through the resistor from the battery Electrons are ‘resisted’ by the resistor The atoms in the resistor gain kinetic energy The resistor gets hot (electrical energy transferred as heat) We can calculate the energy transformed using the equation below: E C V Energy Transformed (J) = Potential Difference (V) x Charge Flow (C)

35 Chapter 7 – Nuclear Physics
What you need to know: Nuclear reactions How does the nucleus of an atom change when it emits and alpha or beta particle How can we represent a nuclear reaction Where does background radiation come from The Discovery of the Nucleus (Higher) How was the Nucleus model of the atom established What other models of the atom were there Nuclear Fission What radioactive isotopes are used in nuclear power stations What is nuclear fission How is nuclear hear produced in a power station What are fission neutrons Nuclear Fusion Where does the Sun’s energy come from What happens during nuclear fusion Why is it difficult to make a nuclear fusion reaction

36 Neutron changes into a proton (neutron lost = proton gained)
Nuclear Reactions Alpha particles have 2 protons and 2 neutrons An unstable particle becomes more stable by emitting an α particle 4 2 α Neutron changes into a proton (neutron lost = proton gained) Electrons is created and emitted -1 β Background radiation: Nuclear weapons testing Nuclear power stations Radioactive rocks – some of which give of radio active gases Gamma radiation (which has no mass) is also given off by unstable nuclei after alpha and beta radiation is given off

37 The Discovery of the Nucleus
John Dalton reintroduced the idea that everything was made of atoms He said atoms were solid spheres of matter that could not be split Thomson adapted Dalton’s model He said that an atom is a positively charged sphere with negative electrons distributed through it (plum pudding model) 1914 the nucleus was discovered Alpha particles in a beam are sometimes scattered through large angles when they are directed at a thin metal foil e.g. gold foil Rutherford’s gold foil experiment, meant the following could be discovered using his results: The nucleus was positively charged as it repels the α particles (like charges repel like magnets) Much smaller than the atom because most α particles pass through it without deflection Where most of the mass of the atom is located The paths the α particles take

38 Nuclear Fission: the splitting of an atomic nucleus
There are two elements, which cause nuclear fission when their nucleus split: Uranium 235 Plutonium 239 When one fission actions occurs, the process repeats until the nucleus becomes stable, a chain reaction takes place Nuclear fission is an un-natural process In a nuclear reactor one neutron per fission (on average) goes on to produce further fission Both used in making nuclear weapons Nuclear Reactor

39 Nuclear Fusion Nuclear Fusion: when two nuclei are forced close enough together so they form a single larger nucleus Inside Fusion Reactors The gas is heated by passing an electric current through it The gas becomes so hot is forms a plasma of nuclei The plasma is contained using a magnetic field to prevent it from touching the container walls When hydrogen nuclei are fused together, helium is formed Energy is required to make nuclear fusion occur Energy is also released when two nuclei are fused together (which could be used to produce electricity) Fusion reactors need to be at very high temperatures before nuclear fusion can take place Fusion takes place in the sun, as the core is so hot it consists of nuclei without electrons resulting in them fusing together when they collide with enough kinetic energy otherwise they will repel each other Fusion reactors are safer than fission reactors as: The products (helium) are not radioactive therefore are stable If the plasma touches the sides it immediately cools, meaning fusion can no longer take place

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