GCSE AQA Physics Paper 1

When a system changes, energy is transferred into or away from the system/between energy stores.

Closed systems = neither matter nor energy can enter or leave the system. 

When energy is transferred to an object, the energy is stored. There are 8 types of energy stores: thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic and nuclear.

Energy can be transferred by heating or by doing work. 

Work done = Energy transferred

Heating - energy is transferred to the water from the kettle's heating element, into the water's thermal energy store.

Two-object system: where two methods of energy transfer have been used.

Movement = energy in an object's kinetic energy store. The greater the object's mass and the faster it's going, the more energy there will be in its kinetic energy store. 

Kinetic energy (J) = 0.5 x mass (kg) x (Speed)squared

Lifting an object causes a transfer of energy to the gravitational potential energy store. The higher the object is lifted, the more energy transferred. 

G.P.E (J) = Mass (kg) x Gravitational Field Strength (N/kg) x Height (m)

Falling objects also causes a transfer from the GPE store to its kinetic energy store.          Energy lost from the GPE store = Energy gained in the kinetic energy store

Stretching an object causes a transfer to its elastic potential energy store. 

Elastic potential energy (J) = 0.5 x Spring Constant (N/m) x Extension (m)

Specific heat capacity = the amount of energy needed to raise the temperature of 1kg of a substance by 1 degrees celcius. 

More energy needs to be transferred to the thermal energy store of some meaterials to increase their temperature than others. e.g. you need 4,200 J to warm 1 kg of water by 1 degrees, yet only 139 J to warm 1 kg of mercury by 1 degrees.

Change in thermal energy = mass (kg) x specific heat capacity (J/kg) x temperature change (degrees)

Conservation of Energy principle = Energy can be transferred usefully, stored or dissipated - however it cannot be created or destroyed 

Dissipated energy may be called "wasted energy" as it's stored in a way that is not useful whatsoever (usually into the thermal energy store). 

E.g. a mobile phone is a system. When you use the phone, energy is transferred from the chemical energy store of the battery in the phone. But some of this energy is transferred to the thermal energy store of the phone. 

Energy transfers for closed systems = A cold spoon is dropped into an insulated flask of hot soup, which is then sealed. This is a closed system as the flask is a perfect thermal insulator. Energy is transferred from the themal energy store of the soup to the useless thermal energy store of the spoon. Energy transfers have occured within the system, but no energy has left. - so the net change in energy is zero. 

Power = the rate of energy transfer/doing work

One watt = 1 joule of energy transferred per second 

Power equations:

Power (W) = Energy transferred (J) / Time (s)

OR Power (W) = Work done (J) / Time (s)

A powerful machine is one which transfers a lot of energy in a short space of time.

CONDUCTION = The process where vibrating particles transfer energy to neighbouring particles. (Only in solids)

Energy transferred to an object by heating is transferred to the thermal store of the object. This energy is shared across the kinetic energy stores of the particles in the object. The particles being heated vibrate more and collide more, causing transfers in the kinetic energy stores. 

CONVECTION = where energetic particles move away from hotter to cooler regions. (Only in liquids and gases)

Energy is transferred by heating to the thermal store of the liquid or gas. When heating a region of a gas or liquid, the particles move faster and the space between individual particles increases. The density decreases too. 

CONVECTION CURRENTS 

The example is a radiator. Energy is transferred from the radiator to the nearby air particles by conduction. The air becomes warmer and less dense, as the particles move quicker. The warm air rises and is replaced by cooler air. It cools, becomes denser and sinks. The cycle repeats, causing a flow of air. 

The less energy wasted in an energy store,the more efficient the device is said to be. 

Efficiency can be increased by insulating, lubricating or streamlining objects.

Efficiency = Useful output energy transfer / Total input energy transfer

Efficiency = Useful power output / Total power output

NO system will ever be 100% efficient as the wasted energy is usefully transferred to a thermal energy store. However, electric heaters are 100% efficient because all energy is transferred from the electrostatic energy store to the thermal energy store.

Non-renewable energy are fossil fuels and nuclear fuel. Fossil fuels are natural and have been formed underground, and are typically burnt to provide energy. Examples include coal, oil and natural gas - they all run out, they do damage to the environment but they provide most energy.

Renewable energy sources will never run out, although they do cause a lot of damage to the environment and they don't provide much energy. Examples include the sun, wind, water waves, bio-fuel, tides, and geothermal. 

Transport uses - non-renewable sources include petrol and diesel (from oil), and coal for old-fashioned trains, which make steam. Renewable sources include vehicles that run on pure biofuels. 

Heating uses - Non-renewable sources include natural gas for heating homes (water and radiators), coal (fireplaces), and electric heaters (electricity). Renewable energy sources geothermal heat pumps, solar water heaters and burnt bio-fuels.

Density (kg/metres cubed) = mass (kg) / volume (metres cubed)

The density of an object depends on what it's made of and the arrangement of particles. Dense materials have particles packed tightly together, whereas less dense are more spread out. 

Three states of matter and their properties:

SOLIDS - Strong forces of attraction hold the particles together in a fixed and arranged position. The particles don't have much energy so they can only vibrate about their fixed positions. The density is highest in this matter.

LIQUIDS - There are weaker forces of attraction between the particles. The particles are close together but can move past each other and form irregular arrangements. They have more energy than the particles in a solid - they move in random directions at low speed. They are less dense than solids.

GASES - Almost no forces of attraction between these particles. The particles have more energy than in liquids and solids- free to move, and travel in random directions at high speeds. Gases have low densities. 

When heating a liquid, it boils and becomes a gas. Heating a solid makes it melt and become a liquid. The state can also change due to cooling.

Here are the changes of state:

HEATING: Solids melt into liquids. Liquid boils or evaporates into a gas. 

COOLING: Solids sublimate into gases. Gases condense into liquids. Liquids freeze into solids

A change of state is a physical change, where you don't end up with a new substance - it's the same substance you began with. Reversing a change of state will also return the substance to its original form and properties. The number of particles doesn't change - they're just arranged differently. Mass is conversed.

Particles in a system vibrate or move around - having energy in their kinetic energy stores. Their positions cause energy in the potential energy stores. The internal energy of a system is the total energy of the particles in both its kinetic and potential energy stores. 

Heating the system transfers energy to particles, increasing the internal energy. This either raises the temperature of the system or produces a change of state.

When a substance is melting or boiling, you're still putting in energy and so increasing the internal energy, but the energy is used for breaking intermolecular bonds rather than raising the temperature. When a substance is condensing or freezing, bonds are forming between particles, releasing energy. The internal energy decreases, but the temperature doesn't go down until all substance has changed. 

Latent Heat = The energy needed to change the state of a substance of a 1kg mass.

Solid to liquid (melting/freezing) = the specific latent heat of fusion. 

Liquid to gas (condensing/boiling/evaporating) = the specific latent heat of vaporization. 

The particles in a gas are constantly moving with random directions and speeds. Increasing the temperature of a gas transfers energy into the kinetic energy stores. The higher the temperature, the higher the average energy. As you increase the temperature of a gas, the average speed of the particles increase. 

When gases move at high speeds, they collide. On collision, they exert a force, increasing pressure. Faster particles and more frequent collisions both lead to an increase in net force, and so gas pressure. Increasing the temperature increases the speed, increasing pressure. 

Alternatively, if temperature is constant, increasing the volume of a gas means that particles get more spread out. The gas pressure decreases. Pressure and volume are inversely proportional - when pressure goes down, volume goes up. (Pressure x Volume = Constant)

Doing work on a gas can increase its temperature. Transferring energy by applying force on a gas increases its internal energy, increasing its temperature. This transfers energy to the kinetic energy stores of the gas particles, increasing the temperature. 

Rutherford's Plum Pudding Model

- 1804, John Dalton found that matter was made up of "tiny spheres", soon named atoms.

- 1905, J.J. Thomson discovered electrons. Thomson suggested that electrons were like fruit in a plum pudding - the plum pudding model.

- IN 1909, Rutherford did an experiment with alpha particles - he fired a beam of them through gold foil. Most particles were expected to pass through the foil, and maybe one deflected. Whilst most did pass through, more were deflected than expected - this is something the plum pudding model couldn't explain. 

- Because a few alpha particles were deflected back, the scientists realised that most of the mass of the atom must be concentrated in the centre, a positively-charged nucleus. 

- Nearly all particles passed through, so most of an atom is empty space.

Isotopes = different forms of the same element. They have the same number of protons but a different number of neutrons, indicating a different mass number. Unstable isotopes tend to decay into other elements and give out radiation to become more stable. This process is called radioactive decay. 

Radioactive substances spit out one or more types of ionising radiation from their nucleus. They can also release neutrons as they rebalance. Ionising radiation knocks off  electrons from atoms, creating positive ions. 

Alpha particles = two neutrons and two protons. They don't penetrate very far into materials and are stopped quickly - they can only travel a few cm in air and are absorbed by a sheet of paper. They are strongly ionising - alpha radiation is where is when an alpha particle is emitted from the nucleus.

Beta particles = A fast moving electron released by the nucleus. They have no mass and a charge of -1. They are moderately ionising, penetrating moderately far into materials before colliding and have a range in air of a few metres. They can be absorbed by aluminium. For every beta particle emitted, a neutron in the nucleus has turned into a proton.

Gamma ray = Waves of electromagnetic radiation released by the nucleus. They penetrate far into materials without being stopped and will travel a long distance through air. This means they're weakly ionising as they tend to pass through rather than collide with atoms. They hit something and do damage. They can be absorbed by thick sheets of lead/concrete.

Background radiation = The low-level radiation that's around us all the time. 

Radioactivity of natural occurring unstable isotopes are all around us - in air, food, building materials and in the rocks under our feet.

Radiation from space, known as cosmic rays. This comes from the sun, but the earth's atmosphere protects us from this. 

The radiation dose risks damage to body tissues due to exposure of radiation.

Exposure to radiation = Irradiation

Contamination = radioactive particles getting onto objects. This is especially dangerous because radiation particles could get inside your body. Gloves and tongs can help.

- Beta and gamma sources are the most dangerous. This is because they can penetrate the body and get to the delicate organs . Alpha can't penetrate, so it's less dangerous. 

- Inside the body, alpha sources are the most dangerous, because they damage in a very localised area. 

Risks of using radiation

- Can enter living cells and ionise atoms and molecules within them. This can lead to tissue damage. 

- Lower doses can give rise to mutant cells which divide uncontrollably (cancer).

- Higher doses can kill all cells causing radiation sickness (vomiting, tiredness, hair loss etc).

Gamma sources and medical tracers - Radioactive isotopes can be injected to track process in the body. One example is iodine-123, absorbed by the thyroid gland just like normal iodine-127, which would indicate whether the thyroid gland is taking in iodine as it should. Whilst this can diagnose illnesses, there is a risk of cancer from one use.

Radiotherapy - High doses of radiation can kill all living cells, so it can be used to treat cancer. Gamma rays are directed at the cancerous cells without damaging too many normal cells. They may be also put next to tumours or inside them. 

Nuclear fission - A type of nuclear reaction that is used to release energy from large and unstable atoms by splitting them into smaller atoms. 

- Spontaneous fission is rare; the nucleus has to absorb a neutron first.

- When the atom splits it forms two new lighter elements that are roughly the same size. 

- Two or three neutrons are are also released when an atom splits. If any of these neutrons are moving slow enough to be absorbed by another nucleus, they can cause more fission. This is a chain reaction.

- The untransferred energy is carried away by gamma rays. 

Nuclear Fusion

The opposite of nuclear fission. Two light nuclei collide at high speed and join to create a larger, heavier nucleus. The heavier nucleus produced by the fusion doesn't have as much mass as the two separate, light nuclei. Some mass is converted to energy, then released as radiation. Fusion releases a lot of energy. The temperatures and pressures are really hard and expensive to build.

Half-life can be used to find the rate at which a source decays (its activity).

Activity is measured in becquerels (Bq) - 1Bq is 1 decay per second.

Half-life = the time taken for the number of radioactive nuclei in an isotope to halve. 

A short half-life is when the activity falls quickly, because the nuclei are very unstable and rapidly decay. They are dangerous because they primarly emit a high amount of radiation. 

A long-half life is when the activity falls more slowly because most of the nuclei don't decay for a long time. This is dangerous as surroundings are exposed to radiation for a long period of time.

Current = The flow of electric charge. In a single closed loop, the current has the same value everywhere in the circuit. Unit = Ampere (A)

Potential difference = The driving force that pushes the charge round. Its unit is the volt, V.

The greater the resistance across a component, the smaller the current that flows.

Resistance = anything that slows the flow down. Unit: Ohm. 

Charge flow (Coulombs) = Current (A) x Time (s)

Potential Difference (V) = Current (A) x Resistance (Ohms)

Ohmic conductor = At a constant temperature, the current flowing through an ohmic conductor is directly proportional to the potential difference across it, so you get a straight line. They have a constant resistance too.

Filament lamp = As the current increases, the temperature of the filament increases, so the resistance increases. This means less current can flow per unit pd, so the graph gets shallower - hence the curve. 

Diode = Resistance depends on the direction of the current. They will happily let current flow in one direction, but have a very high resistance in the reverse direction.

LDR = Light Dependent Resistor. In bright light, the resistance falls. In darkness, the resistance is highest. They have lots of applications including automatic night lights, outdoor lighting and burglar detectors.

Thermistor = A temperature dependant resistor. In hot conditions, the resistance drops. In cool conditions, the resistance goes up. Thermistors make useful temperature detectors, e.g. car engine and electronic thermostats.

- In series circuits, the different components are connected in a line, end to end, between the positive and negative of the power supply (except for voltmeters, which are always connected in parallel).

- Removing or disconnecting one component will stop the circuit. 

Potential difference = PD is shared. V(total) = V1+V2+V3

Current = In series circuits, the same current flows through all components. The size of the current is determined by the total pd of the cells and the total resistance of the circuit. 

Resistance = Adds up - the total resistance is the sum of the resistances. This is because by adding a resistor in series, the two resistors have to share the total PD. The PD across each resistor is lower, so the current is low too. The bigger a component's resistance, the bigger its share of the total potential difference. 

- In parallel circuits, each component is separately connected to the +Ve and -Ve of the supply (except ammeters, which are always connected in series). 

- Removing or disconnecting one of them will hardly affect the others at all.

Potential difference = The same across all components. All components get the full source pd. V1 = V2 = V3 etc.

Current = The total current flowing around the circuit is equal to the total of all the currents through the separate components. I(total) = I1 + I2 + .. etc.

Adding a resistor in parallel reduces the total resistance. In parallel, both resistors have the same potential difference. But by adding another loop, the current has more than one direction to go in. This increases the total current that can flow around the circuit. 

Using V = IxR, an increase in current means a decrease in the total resistance of the circuit.

Alternating current = The current is constantly changing direction. Alternating currents are produced by alternating voltages, where the positive and negative ends keep alternating.

The UK mains supply is an AC at around 230V.

The frequency of the AC mains supply is 50Hz (cycles per second).

Direct current = A current that is always flowing in the same direction, created by direct voltage.

THE THREE SEPARATE WIRES

Neutral Wire (blue) = Completes the circuit and and carries away current - electricity normally flows in through the live wire and out through the neutral wire.

Live Wire (brown) = The live wire provides the alternating potential difference from the mains supply.

Earth Wire (green and yellow) = Used for protecting the wiring and safety - stops the appliance from becoming live. It doesn't usually carry a current, only when there's a fault.

- A moving charge transfers energy, as the charge does work against the resistance of the circuit.

E.g. Kettles transfer energy electrically from the mains ac supply to the thermal energy store of the heating element inside the kettle. 

E.g. Energy is transferred electrically from the battery of a handheld fan to the kinetic energy store of the fan's motor.

Energy transferred depends on the power: 

Energy transferred (J) = Power (W) x Time (s)

E = Pt

Energy transferred (J) = Charge flow (C) x Potential Difference (V)

The battery with a bigger PD will supply more energy to the circuit for every coulomb of charge which flows round it, because the charge is raised up "higher" at the start.

The national grid = A giant system of cables and transformers that covers the UK and connects power stations to consumers. 

Electricity production has to meet demand, e.g. when a lot of power is used when a sporting final is shown on a TV. 

The national grid uses a High PD and a Low Current. Having a high current makes you lose loads of energy as the wires heat up and energy is transferred to the thermal energy store. It's also much cheaper to boost the PD up really high and keep the current as low as possible. 

Getting the PD up requires big transformers (pylons), although it is still cheaper. The PD is increased using a step-up transformer, and then reduced by a step-down transformer.

 When certain insulating materials are rubbed together, negatively charged electrons will be scraped off one and dumped on the other. This leaves the materials electrically charged - a positive charge on one material and a negative charge on the other. Only electrons move - never positive charges.

Opposite electric charges are attracted to each other, while two things with the same electric charge will repel each other. These forces get weaker when further apart.

SPARKS

If the static charge on an object is very large, electrons may jump across the gapfrom the charged objectto a nearby conductor. This causes a spark, which can be dangerous.

The greater the charge on the object, the greater the voltage/potential difference is. If the voltage is too high, a current will flow to the object and might cause a spark.

The problem is overcome by earthing the object. This means joining the object to a large metal plate in the ground by a conducting wire so any charge just flows to the earth, and the object’s charge is lost.