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AQA - GCSE Physics Revision

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AQA - GCSE Physics Revision

Additional Physics (P2)

- 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

- 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)

- 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

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*

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

- 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

- Forces Between Objects

Upthrust

Forces can:

Twist

Pull

Push

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

Friction

Thrust

Weight/Gravity

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

Force

- Acceleration depends on:
- The mass of an object
- The amount of force applied

F

Resultant Force (N) = Mass (kg) x Acceleration (m/s²)

M

A

Mass

Acceleration

- 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

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

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 equalthe object reaches a terminal velocity (the resultant force is 0 so the acceleration is 0)

- 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

- 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

Work Done

Gravitational Potential Energy

Work Done/Energy Transferred (J) = Force (N) x Distance (M)

W

G

F

W

D

H

Force

Weight

Height

Distance

Change of Gravitational Potential Energy(J) = Weight (N) x Change in Height (M)

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

Momentum: the ability for an object to keep moving (relating its mass and velocity) in the same direction

Mass in motion

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

P

M

V

- 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

Mass

Velocity

The momentum of a moving object(Kg m/s) = Mass (Kg) x Velocity (m/s)

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

- 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

- Electrical Charges

- 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

- Van de Graaff Generator
- 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

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)

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

- 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

- Electric Circuits

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

Resistance (ohms) = Potential difference (volts)

Current (amperes)

Ammeter: connected in series with the lamp to measure the current going through the lamp

The current through a resistor of a constant temperature is directly proportional to the potential difference across the resistor

Voltmeter: connected in parallel to measure the potential difference across the lamp

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

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

- 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

- Alternating Current

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)

Frequency = 1

Time (sec)

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

Live Wire – is brown and connected to the live pin

The pins in a plug are made of brass

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

Neutral– is blue and connected to the neutral pin

The case of the plug is made out of stiff plastic

The cable is copper but is surrounded by an insulator such as rubber/flexible 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

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

Power: energy transferred per second

The power (watts) is the energy transformed (joules) every second, using the equation below:

Power (W) = Energy (J)

Time (S)

E

P

We can also calculate power dissipated (lost) in a device, using the equation below:

P

V

T

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)

Electrical Current: the rate of flow of charge (measured in Coulomb [C])

The charge of an appliance can be calculated using the equation below:

Charge Flow (C) = Current (A) x Time (S)

Current

C

E

C

T

V

I

We can calculate the energy transformed using the equation below:

Energy Transformed (J) = Potential Difference (V) x Charge Flow (C)

- 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

- Nuclear reactions

Alpha particles have 2 protons and 2 neutrons

An unstable particle becomes more stable by emitting an α particle

4

0

α

β

2

-1

Neutron changes into a proton (neutron lost = proton gained)

Electrons is created and emitted

- 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

- 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

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

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