Physics Paper 1 AQA NEW SPEC

What is a system?

  • A system is an object or group of objects. 
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Give 8 examples of energy stores.

  • Thermal energy - describes the energy a substance has because of its temperature.
  • Kinetic energy - describes the energy an object has because it is moving. 
  • Graviational potential energy - describes the energy stored in an object because of its position, such as an object above ground.
  • Elastic potential energy - describes the energy stored in a springy object when you stretch or squash it.
  • Chemical energy - includes foods, fuels or the chemicals found in batteries. The energy is transferred during chemical reactions.
  • Magnetic energy
  • Electrostatic energy
  • Nuclear energy
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What happens when a system changes?

  • There are changes in the way energy is stored when a system changes. 
  • When a system changes, energy is transferred. It can be transferred into or away from the system, betweeen different objects in the system or between different types of energy stores.
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What is a closed system?

  • Closed systems are systems where neither matter nor energy can enter or leave.
  • The net change in the total energy of a closed system is always zero.
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How is energy transferred in a torch?

  • In a torch, the torch's battery pushes a current through the bulb. This makes the torch emit light, and also get hot. 
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How is energy transferred in a kettle?

  • Energy is transferred to the water - which could be the system - from the kettle's heating element by heating, into the water's thermal energy store, causing the temperature of the water to rise.
  • This process could also be described as a two object system, where the kette's heating element and the water act as the two object system. Energy is transferred electrically to the thermal energy store of the kettle's heating element, which transfers energy by heating to the water's thermal energy store.
  • When an electric kettle is used to boil water, the current in the kettle's heating element transfers energy to the thermal energy store of the water and the kettle.
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How can falling objects transfer energy?

  • When an object is thrown into the air, the object slows down as it goes up. 
  • Here, energy is transferred from the object's kinetic energy store to it's gravitational potential energy store.
  • When an object is dropped from a height, it is accelerated by gravity. The gravitational force does work. 
  • As it falls, energy from the gravitational potential energy store is transferred to its kinetic energy store. 
  • For a falling object when there's no air resistance:
  • Energy lost from the gravitational potential energy store = energy gained from the kinetic energy store.
  • In real life, air resistance acts against all falling objects - it causes some energy to be transferred to the other energy stores.
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Describe a flow diagram for chemical energy store.

Chemical energy store in batteries -> electric current in wires -> energy transferred to the surroundings -> light waves and an increase in the thermal energy store of the surroundings.

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Describe a flow diagram for G.P.E.

Gravitational potential energy store -> kinetic energy store -> energy transfer to the surroundings -> sound waves and an increase in thermal energy store of the surroundings.

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How can energy be transferred by doing work?

  • Work done is another way of saying energy transferred.
  • Work can be done when the current flows - where work is done against resistance in a circuit.
  • Eg:
  • Throwing a ball upwards: the initial force exerted by a person to through a ball upwards does work. It causes an energy transfer from the chemical energy store of the person's arm to the kinetic energy store of the ball and arm.
  • Car moving on a road: the friction between a car's brakes and its wheels does work as the car slows down down. It causes an energy transfer from the wheel's kinetic energy stores to the thermal energy stores of the surroundings.
  • Car colliding: in a collision between a car and a stationary object, the normal contact force between the car and the object does work. It causes energy to be transferred from the car's kinetic energy stores, eg. the elastic potential and thermal energy stores of the object and the car body. Some energy may also be transferred away by sound waves.
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Formula for kinetic energy.

kinetic energy = 0.5 × mass × (speed)²

OR

kinetic energy = 1/2 x m x v²

  • kinetic energy in joules, J
  • mass, m, in kilograms, kg
  • speed, v, in metres per second, m/s
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Formula for elastic potential energy.

Assumes that the limit of proportionality has not been exceeded.

elastic potential energy = 0.5 × spring constant × (extension)²

OR

elastic potential energy = 1/2 x k x (e)²

  • elastic potential energy, Ee , in joules, J
  • spring constant, k, in newtons per metre, N/m
  • extension, e, in metres, m
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Formula for gravitational potential energy.

g.p.e. = mass × gravitational field strength × height

OR

g.p.e = mgh

  • gravitational potential energy, E p, in joules, J
  • mass, m, in kilograms, kg
  • gravitational field strength, g, in newtons per kilogram, N/kg (In any calculation the value of the gravitational field strength (g) will be given.)
  • height, h, in metres, m
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What is specific heat capacity?

  • The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.
  • How much energy a substance can store.
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What is the formula for specific heat capacity?

change  in thermal energy = mass  × specific heat capacity × temperature change

OR

∆ E = m c ∆ θ

  • change in thermal energy, ∆E, in joules, J
  • mass, m, in kilograms, kg
  • specific heat capacity, c, in joules per kilogram per degree Celsius, J/kg °C
  • temperature change, ∆θ, in degrees Celsius, °C 
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REQUIRED PRACTICAL - SHC.

1) To investigate a solid material, you'll need a block of the material with two holes in it for the heater and thermometer to go into.

2) Measure the mass of the block and then wrap it in an insulating layer to reduce the energy transferred from the block to the surroundings. Insert the thermometer and heater.

3) Measure the initial temperature of the block and set the potential difference, V, of the power supply to be 10 V. Turn on the power supply and start a stopwatch.

4) When the power is turned on, the current in the circuit (the moving charges) does work on the heater, transferring energy electrically from the power supply to the heater's thermal energy store. This energy is then transferred to the material's thermal energy store by heating, causing the material's temperature to increase.

5) As the block heats up, use the thermometer to measure its temperature every minute. Keep an eye on the ammeter - the current through the circuit shouldn't change.

6) When you've collected enough readings, turn off the power suppy. Work out SHC.

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REQUIRED PRACTICAL - Apparatus in SHC.

  • Power supply - connects the ammeter from one hole and the other hole connects to the heater.
  • Ammeter - is connected to the power supply.
  • Block of material - has two holes for the thermometer and heater to be placed in and is wrapped under insulation.
  • Insulation - wraps around the block of material.
  • Thermometer - is placed in one of the holes of the block of material.
  • Heater - is placed in one of the holes of the block of material.
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What is power?

  • Power is defined as the rate at which energy is transferred or the rate at which work is done.
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What are the two formulas for power?

Power = energy transferred / time.

  • power, P, in watts,
  • W energy transferred, E, in joules, J
  • time, t, in seconds, s

Power = work done / time.

  • power, P, in watts, W
  • work done, W, in joules, J
  • time, t, in seconds, s

The two formulas are connected: an energy transfer of 1 joule per second is equal to a power of 1 watt. In other words... One watt = 1 joule of energy transferred per second.

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Describe the conservation of energy principle.

  • Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.
  • Energy is dissipated, so that it is stored in less useful ways. This energy is often described as being ‘wasted’.
  • For example: 
  • A mobile phone is a system. When you use the phone, energy is usefully transferred from the chemical energy store of the battery in the phone. But some of this energy is dissipated in this transfer to the thermal energy store of the phone. 
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Describe energy transfers in a closed system.

  • There is no net change to the total energy.
  • For example:
  • A cold spoon is dropped into an insulated flask of hot soup, which is then sealed. You can assume that the flask is a perfect thermal insulator so the spoon and the soup form a closed system. Energy is transferred from the thermal energy store of the soup to the useless thermal energy store of the spoon (causing the spoon to cool down slightly). Energy transfers have occured within the system, but no energy has left the system. 
  • This shows that the net change is 0.
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The higher the thermal conductivity...

  • The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material.
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What is conduction?

  • Occurs mainly in solids.
  • Conduction is the process where vibrating particles transfer energy to neighbouring particles.
  • Energy is transferred to an object by heating is transferred to the thermal energy store of the object. The energy is shared across the kinetic energy stores of the particles in the object.
  • The particles in the part of the object being heated vibrate more and collide with each other. These collisions cause energy to be transferred between particles' kinetic energy stores. This is conduction. 
  • The process contiues throughout the object until energy is transferred to the other side of the object. It's then usually transferred to the thermal energy store of the surroundings (or anything else touching the object).
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What is thermal conductivity?

  • Thermal conductivity is a measure of how quickly energy is transferred through a material in the way.
  • Materials with a high thermal conductivity transfer energy between their particles quickly.
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What is convection?

  • Occurs only in liquids and gases.
  • Convection is where energetic particles move away from hotter regions to cooler regions.
  • Energy is transferred by heating to the thermal store of the liquid or gas. 
  • As with conduction, the energy is shared across the kinetic energy stores of the gas or liquid particles. 
  • Unlike in solids, the particles in liquids and gases are able to move. When you heat a region of a gas or a liquid, the particles move faster and the space between the individual particles increases. 
  • This causes the density of the region being heated to decrease.
  • Because liquids and gases can flow, the warmer and less dense region will rise above denser, cooler regions. 
  • If there is a constant heat source, a convection current can be created.
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How do radiators create convection currents?

  • Heating a room with a radiator relies on creating convection currents in the air of the room. 
  • Energy is transferred from the radiator to the nearby air particles by conduction (the air particles collide with the radiator surface).
  • The air by the radiator becomes warmer and less dense - the particles move quicker.
  • The warm air rises and is replaced by cooler air. The cooler air is then heated by the radiator. 
  • At the same time, the previously heated air transfers energy to the surroundings. It cools, becomes denser and sinks.
  • The cycle repeats, causing a flow of air to circulate around the room - this is a convection current.
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What does lubrication reduce?

  • Lubrication reduces frictional forces.
  • Whenever something moves, there's usually at least one frictional force acting against it. This causes some energy in the system to be dissipated, eg. air resistance can transfer energy from a falling object's kinetic energy store to its thermal energy store.
  • For objects that are being rubbed together, lubricants can be used to reduce the friction between the object's surfaces when they move. 
  • Lubricants are usually liquids (like oil) so they can flow easily between objects and coat them. 
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General ways to prevent energy loss.

  • Having thick walls that are made from a material with a low thermal conductivity. The thicker the walls and the lower their thermal conductivity, the slower the rate of energy transfer, so the building will cool more slowly.
  • Use thermal insulation.
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Give examples of thermal insulation in houses.

Cavity walls:

  • Made up of an inner and outer wall with an air gap in the middle. The air gap reduces the amount of energy transferred by conduction through the walls. 
  • Cavity wall insulation, where the cavity wall air gap is filled with a foam can also reduce energy transfer by convection in the wall cavity.

Loft insulation:

  • Can be laid out across the loft floor and ceiling. Fibreglass wool is often used and is a good insulator as it has pockets of trapped air. Reduces energy loss by conduction and also helps prevent convection currents from being created. 

Double glazed windows:

  • Have an air gap between two sheets of glass to prevent energy transfer by conduction through the windows.

Draught excluders:

  • Around doors and windows which reduces energy transfers by convection.
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REQUIRED PRACTICAL - Effectiveness of insulators.

1) Boil water in a kettle. Pour some of the water into a sealable container (eg. beaker and a lid) to a safe level. Measure the mass of water in the container. 

2) Use a thermometer to measure the intial temperature of the water.

3) Seal the container and leave it for 5 minutes. Measure this using a stopwatch.

4) Remove the lid and measure the final temperature of the water. 

5) Pour away the water and allow the container to cool to room temperature. 

6) Repeat this experiment, but wrap the container in a different material once it has been sealed. Make sure that you add the same mass of water each time. 

You should find that the temperature difference (and so the energy transferred) is reduced by wrapping the container in thermally insulating materials like bubble wrap or newspaper.

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What factor affects how good an insulating materia

  • The thickness of the material affects the temperature change of the material according to the required practical on investigating effectiveness of different insulators.
  • The thicker the insulating layer, the less energy is transferred and the smaller the temperature change of the water.
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What are the two equations for efficiency?

Efficiency = useful output energy transfer / total input energy transfer

Efficiency = useful power output / total power input

You can give the efficiency as a decimal or you can multiply your answer by 100 to get a percentage.

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Increase the efficiency of an intended energy tran

  • Insulating objects
  • Lubricating objects
  • Making objects more streamlined
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Useful energy input not equal to output?

  • No device is 100% efficient - wasted energy is usually transferred to useless thermal energy stores.
  • Electric heaters are an exception, usually 100% efficient because all the energy in the electrostatic energy store is transferred to the useful thermal energy store.
  • Ultimately, all energy ends up transferrred to the thermal energy stores. For eg. if you use an electric drill, its energy is transferred to lots of different energy stores, but quickly ends up in thermal energy stores.
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What are renewable energy resources?

  • A renewable energy resource is one that is being (or can be) replenished as it is used.

Examples:

  • Solar - sun
  • Wind
  • Water waves
  • Hydro-electricity 
  • Bio-fuel
  • Tides 
  • Geothermal

These will never run out, the energy can be 'renewed'. Most of them do damage the environment, only in less nasty ways than non-renewables. The only trouble is, they don't provide much energy and some of them are unreliable because they depend on the weather.

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What are non-renewable energy resources?

  • A non-renewable energy resource is one that is not being replenished as it is used.

Examples:

  • Coal - Fossil fuel
  • (Natural) Gas - Fossil fuel
  • Oil - Fossil fuel
  • Nuclear fuel

They will all 'run' out one day, damage the environment but they provide most of our energy.

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List the ways in which energy resources can be use

The uses of energy resources include: transport, electricity generation and heating.

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How are energy resources used for transport?

Renewable:

  • Vehicles than run on pure bio-fuels or a mix of a bio-fuel and petrol or diesel (only the bio-fuel bit is renewable).

Non-renewable:

  • Petrol and diesel powered vehicles (including most cars) use fuel created from oil.
  • Coal is used in some old fashioned steam trains to boil water to produce steam.
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How are energy resources used for heating?

Renewable:

  • A geothermal (or ground source) heat pump uses geothermal energy resources to heat buildings.
  • Solar water heaters work by using the sun to heat water which is then pumped into radiators in the building.
  • Burning bio-fuel or using electricity generated from renewable resources can also be used for heating.

Non-renewable:

  • Natural gas is the most widely used fuel for heating homes in the UK. The gas is used to heat water, which is then pumped into radiators throughout the home.
  • Coal is commonly burnt in fireplaces.
  • Electric heaters (storage heaters) which use electricity generated from non-renewable energy resources.
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Describe a plane journey in terms of energy transf

  • At the start of a plane journey the fuel tank is full.
  • The fuel = chemical energy store.
  • When the plane is not moving, it has 0 kinetic energy store.
  • As it starts to move, the chemical energy store is converted into a kinetic energy store.
  • At lift off, the graviational potential store starts to increase as the chemical store of the fuel starts to decrease. 
  • Eventually, all of the chemical store in the fuel is transferred to the surroundings via heating and waves.
  • As the plane lands, the gravitational potential store will decrease.
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Pros and cons of Wind Power.

Each turbine has a generator inside it - the rotating blades turn the generator and produce electricity. 

Advantages:

  • There's no pollution.
  • No fuel costs and minimal running costs.
  • No permanent damage to the landscape.

Disadvantages:

  • Pollution is involved with manufacturing the turbines.
  • They spoil the view - about 1500 wind turbines are needed to replace 1 coal-fired power station and 1500 covers a lot of gound which has a big effect on the scenery.
  • They can be very noisy, which would be a disturbance for anyone living nearby.
  • Turbines are highly dependent on the weather. If winds stop blowing, the turbines stop. If the winds are too strong, and it's impossible to increase supply when there's extra demand. Produce electricty 70-85% of the time.
  • Initial costs are quite high.
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Pros and cons of Solar Cells.

Generate electricity directly from sunlight.

Advantages:

  • Best source of energy to charge batteries in calculators and watches, don't use much energy.
  • Often used in remote places where they have no choice (Australian outback) and to power electric road signs and satellites.
  • No pollution.
  • Sunny country = reliable source of energy but in day time only.
  • Energy is free and has low running costs.

Disadvantages:

  • Pollution from manufacturing.
  • Cost-effectie in cloudy countries like Britain.
  • Can't increase the power output when there's extra demand.
  • Initial costs are high.
  • Generates electricity on a small scale.
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Pros and cons of Geothermal Power.

Use energy from underground thermal energy stores.

Advantages:

  • Free, reliable energy.
  • Very few environmental problems.
  • Can be used to generate electricity or to heat buildings directly.

Disadvantages:

  • Only possible in volcanic areas where hot rocks lie near to the surface. Source most of the energy is the slow decay of radioactive elements like uranium, deep inside the Earth.
  • There aren't many suitable locations for power plants.
  • Cost of building a power plant is often high compared to the amount of energy it produces.
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Pros and cons of Hydro-electric Power.

Transfers energy from the kinetic store of falling water. Requires flooding of a valley by building a dam. Rainwater is caught and allowed out through turbines.

Advantages:

  • No pollution.
  • Putting hydro-electric power stations in remote valleys tends to reduce their impact on humans.
  • Provides an immediate response to an increased demand for electricity.
  • No problems with reliability - except in times of drought which is unlikely in Britain.
  • No fuel costs or running costs.
  • Can generate electricity on a small scale in remote areas.

Disadvantages:

  • Big impact on environment due to flooding of the valley (rotting vegetation releases methane and carbon dioxide) and possible loss of habitats for some species (sometimes the loss of whole villages).
  • Reservoirs can look very unsightly when they dry up.
  • Initial costs are high.
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Pros and cons of Wave Power.

Lots of small wave-powered turbines located around the coast.

Advantages:

  • No pollution.
  • No fuel costs and minimal running costs.
  • Usefull on small islands.

Disadvantages:

  • Disturbs the seabed and the habitats of marine animals, spoiling the view and being a hazard to boats.
  • Unreliable, waves tend to die out when the wind drops.
  • Initial costs are high.
  • Can't produce energy on a large scale.
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Pros and cons of Tidal Barrages.

Tidal Barrages are big dams built across river estuaries with turbines in them. As the tide comes in, it fills up the estuary. Water is then allowed out through the turbines at a controlled speed. Pulled by the gravitational pull of the sun and moon.

Advantages:

  • No pollution.
  • Reliable - can happen twice a day without fail and always near to the predicted height.
  • No fuel costs and minimal running costs.
  • Even though it can only be used in some of the most suitable estuaries, tidal power has the potential fo generating a signifcant amount of energy.

Disadvantages:

  • Problems with preventing free access by boats, spoiling the view and altering the habitat of the wildlife.
  • The height of the tide is variable so lower tides will provide significantly less energy than the bigger tides.
  • Don't work when the water level is the same on either side of the barrage - can happen four times a day because of the tides.
  • Initial costs are high.
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Pros and cons of Bio-fuels.

Renewable energy resource created from either plant products or animal dung. Can be solid, liquid or gas and can be burnt to produce electricity or run cars in the same ways as fossil fuels.

Advantages:

  • Carbon neutral - only true if you keep growing plants at the same rate as burning things.
  • Reliable - crops take a short time to grow and different crops can be grown all year around.
  • To deal with being unable to respond to immediate energy demands, bio-fuels are continuously stored for when they are needed.

Disadvantages:

  • Cannot respond to immediate energy demands.
  • Costs to refine bio-fuels so they are suitable for use is very high.
  • People worry that growing crops specifically for bio-fuels will mean that there isn't enough space or water to meet the demands for crops that are grown for food.
  • In some regions, large areas of forests have been cleared to make room to grow bio-fuels, reulting in a loss of habitats for species. The decay and burning of this vegetation also increases carbon dioxide and methane emissions.
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Advantages of non-renewable energy resources.

  • Fossil fuels and nuclear energy are reliable. Currently, there's enough fossil and nuclear fuels to meet demand. They are extracted from the Earth at a fast enough rate that power plants always have fuel in stock. Power plants can respond quickly to changes in demand.
  • The running costs aren't expensive. Combined with fairly low fuel extraction costs, using fossil fuels is a cost-effective way to produce energy which makes it popular.
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Disadvantages to non-renewable energy resources.

  • Coal, oil and gas release carbon dioxide into the atmosphere when burnt. All the carbon dioxide adds to the greenhouse effect and contributes to global warming.
  • Burning coal and oil also releases sulfur dioxide, which causes acid rain which can be harmful to trees and soils and can have far-reaching effects in ecosystems.
  • Acid rain can be reduced by taking the sulfur out before the fuel is burned or cleaning up emissions.
  • Views can be spoilt by fossil fuel power plants, and coal mining makes a mess of the landscape, especially "open-cast mining".
  • Oil spillages causes serious environmental problems, affecting mammals and birds that live in and around the sea. Even though we try to avoid them, they usually always happen. 
  • Nuclear power is clean, but the nuclear waste is very dangerous and difficult to dispose of.
  • Nuclear fuel (eg. uranium or plutonium) is cheap but the overall cost of nuclear power is high due to the cost of the power plant and final decommissioning.
  • Nuclear power always carries the risk of a major catastrophe like the Fukushima disaster in Japan.
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What are we currently depending on?

  • Over the 20th century, the electricity use of the UK hugely increased as the population grew and people began to use electricity for more and more things.
  • Since the beginning of the 21st century, electricity use in the UK has been decreasing as we get better at making appliance more efficient and becoming more careful with energy we use in our homes.
  • Most of our energy is produced using fossil fuels (mainly coal and gas) and from nuclear power.
  • Generating electricity isn't the only reason we burn fossil - oil (diesl and petrol) is used to fuel cars, and gas is used heat homes and cook food.
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What is the aim with renewable energy use?

  • The aim is to increase renewable energy use. The UK aims to use renewable resources to provide 15% of its total yearly energy by 2020. The moe has been triggered by:
  • Burning fossil fuels is very damaging to the environment. This makes many people want to use more renewable energy resources that affect the environment less.
  • People and governments are also becoming increasingly aware that non-renewables will run out one day. Many people think it's better to learn to get by without non-renewables before this happens.
  • Pressure from other countries and the public has meant that governments have begun to introduce targets for using renewable resources. This in turn puts pressure on energy providers to build new power plants that use renewable resources to make sure they do not lose business and money.
  • Car companies have also been affected by this change in attitude towards the environment. Electric cars and hybrids (cars powered by two fuels, eg. petrol and electricity) are already on the market and their popularity is increasing.
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What are the limitations of the use of renewables?

  • Limited by reliability, money and politics. Lots of scientific evidence supporting renewables but although scientists can give advice, they don't have the power to make people, companies or governments change their behaviour.
  • Building new renewable power plants costs money, so some energy providers are reluctant to change, especially when fossil fuels are cost-effective. The cost of switching to renewable power will have to be paid, either by costumers in their bills, or through government and taxes. Some people don't want to or can't afford to pay, and there are arguments about whether it's ethical to make them.
  • Even if new power plants are built, there are arguments over where to put them. Eg. some people don't want to live next to a wind farm which could lead to protests. There are arguments over whether it's ethical to make people put up with wind farms built next to them when they may not agree with them.
  • Some energy resources like wind power are not as reliable as traditional fossil fuels, whilst others cannot increase their power output on demand. This would mean either having to use a combination of different power plants (which could be expensive) or researching ways to improve reliability.
  • Research on improving reliability and cost of renewables takes time and money - it may be years before improvements are made, even with funding. Until then, non-renewable energy is necessary.
  • Making personal changes can also be quite expensive. Hybrid cars are generally more expensive than equivalent petrol cars and things like solar panels for you homes are expensive too. The cost of these is slowly going down, but they are still not an option for many people.
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Circuit diagrams.

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What must happen for electrical charge to flow?

  • For electrical charge to flow through a closed circuit the circuit must include a source of potential difference.
  • Electric current is a flow of electrical charge.
  • The size of the electric current is the rate of flow of electrical charge.
  • In a closed, single loop, the current has the same value everywhere. 
  • Potential difference or voltage is the driving force that pushes the charge around.
  • Resistance is anything in the circuit that slows the flow down. 
  • The current flowing through a component depends on the potential difference across it and the resistance of the component.
  • The greater the resistance across a compound, the smaller the current that flows through it (for a given potential difference across the circuit).
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What is the equation for charge, current and time?

charge flow = current × time

OR

Q = I t

  • charge flow, Q, in coulombs, C
  • current, I, in amperes, A (amp is acceptable for ampere)
  • time, t, in seconds, s
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Equation for current, resistance and potential dif

potential difference  = current × resistance

OR

V = I R

  • potential difference, V, in volts, V
  • current, I, in amperes, A (amp is acceptable for ampere)
  • resistance, R, in ohms, Ω
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Ohmic conductors, filament lamps and diodes.

  • Ohmic conductors have a constant resistance
  • The resistance of ohmic conductors doesn't change with the current. At a constant temperature, the charge flowing through an ohmic conductor is directly proportional to the potential difference across it. (R is constant in V=IR).
  • The resistance of some resistors and components does change, eg. a filament lamp or a diode.
  • When an electrical charge flows through a filament lamp, it transfers some energy to the thermal energy store of the filament lamp, which is designed to heat up. Resistance increases with temperature, so as the current increases, the filament lamp heats up more and the resistance increases.
  • For diodes, the resistance depends on the direction of the current. They will happily let current flow in one direction, but have a high resistance if it is reversed.
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REQUIRED PRACTICAL - Investigating resistance fact

1) Attach a crocodile clip to the wire, level with 0 cm on the ruler.

2) Attach the second crocodile clip to the wire, eg. 10 cm away from the first clip. Write down the length of the wire between the two clips.

3) Close the switch, then record the current through the wire and the potential difference across it.

4) Open the switch, then move the second crocodile clip. eg. another 10 cm away from the first clip. Close the switch again and record the new length, current and potential difference.

5) Repeat this for a number of different lengths of the test wire.

6) Use your measurements of current and potential difference to calculate the resistance of each length of wire, using R=V/I.

7) Plot a graph of resistance against length wire and draw a line of best fit. Graph shpuld be directly proportional to the length - the longer the wire, the greater the resistance. If your graph doesn't go through the origin, it could be because your first clip isn't attached exactly at 0 cm, so all of your length readings are out. This is called a systematic error.

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REQUIRED PRACTICAL - Components I-V.

1) Set up the test circuit, with a ammeter, component and variable resistor connected in series, and the voltmeter attached to the component only.

2) Begin to vary the variable resistor. This alters the current flowing through the circuit and the potential difference across the component. 

3) Take several pairs of readings from the ammeter and voltmeter to see how the potential difference across the component varies as the current changes. Repeat each reading twice more to get an average potential difference at each current.

4) Swap over the wires connected to the cell, so the direction of the current is reversed.

5) Plot a graph of current against voltage for the component.

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Describe an ohmic conductor graph.

Image result for ohmic conductor graph (http://www.bbc.co.uk/staticarchive/2c0973c4fe5e0e12f0752d8ac584e1143ea92b9f.gif)

  • The current through an ohmic conductor (at constant temperature) is directly proportional to the potential difference, it is linear and it is a straight line.
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Describe a filament lamp graph.

current on the y axis and voltage on the x axis. A slightly curved line goes through the graph at 45 degrees. (http://www.bbc.co.uk/staticarchive/2453c6b9be954f055256d4a8f6315f29cc169f87.gif)

  • As the temperature increases, the temperature of the filament lamp increases, so the resistance increases. This means that less current can flow per unit pd, so the graph becomes shallower which causes the curve. Not directly proportional and non-linear.
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What is ohm's law?

The current flowing through a resistor at a constant temperature is directly proportional to the voltage across the resistor. So, if you double the voltage, the current also doubles. This is called Ohm's Law.

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Describe a diode graph.

(http://www.bbc.co.uk/staticarchive/3d7f97a63fc5c1682ab84028a60ca4bfecb49aa6.gif)

  • Current will only flow through a diode in one direction because the diode has a very high resistance in the reverse direction.
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Light dependent resistor graph.

Image result for ldr graph

A LDR resistor is dependent on light intensity. Bright light = resistance falls. Darkness = resistance is highest. Automatic lnight light, outdoor light and burglar detectors.

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Thermistor resistance graph.

Image result for thermistor resistance graph

  • A thermistor is a temperature dependent resistor. Hot = resistance dropped. Cool = resistance increases. 
  • Temperature detectors, eg. car engine temperature sensors and electronic thermostats.
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How to use LDRs and thermistors in sensing circuit

  • Sensing circuits can be used to turn on or increase the power to components depending on the conditions they are in. It can be used to operate a fan.
  • The thermistor, fixed resistor and battery are connected in series, with the fan connected to the fixed resistor only.
  • The fixed resistor and the fan will always have the same potential difference across them because they are connected in parallel. 
  • The potential difference of the power supply is shared out between the thermistor and the loop made up of the fixed resistor and the fan according to their resistances - the bigger a component's resistance, the more of the potential difference it takes.
  • As the room gets hotter, the resistance of the thermistor decreases and it takes a smaller share of the potential difference from the power supply. So the potential difference across the fixed resistor and the fan arises, making the fan go faster.
  • You can connect the component across the variable resistor instead of across the fixed resistor.
  • For example, if you connect a bulb in parallel to an LDR, the potential difference across both the LDR and the bulb will be high when it's dark and the LDR's resistance is high.
  • The greater the potential difference across a component, the more energy it gets. So a bulb connected across an LDR would get brighter as the room got darker.
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Describe a typical series circuit.

  • there is the same current through each component
  • the total potential difference of the power supply is shared between the components. 
  • the total resistance of two components is the sum of the resistance of each component.
  • Rtotal = R1 + R2 resistance, R, in ohms, Ω
  • the cell potential differences add up, for eg. when two batteries of 1.5 V are connected, the total potential difference is 3 V.
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Describe a typical parallel circuit.

  • the potential difference across each component is the same. V1=V2=V3....
  • the total current through the whole circuit is the sum of the currents through the separate components, in other words, the current is shared. ITOTAL=I1+12.....
  • the total resistance of two resistors is less than the resistance of the smallest individual resistor.
  • in parallel circuits, each component is separately connected to the +ve and -ve of the supply, except for ammeters which are always connected in series.
  • if you remove/disconnect one of them, it will hardly affect the others at all. 
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What does adding a resistor in parallel reduce?

  • Reduces total resistance. 
  • If you have two resistors in parallel, their total resistance is less than the resistance of the smallest of the two resistors:
  • In parallel, both circuits have the same potential difference across them as the source.
  • This means that the 'pushing force' making the current flow is the same as the source potential difference for each resistor that you add.
  • But, by adding another the loop, the current has more than one direction to go in.
  • This increases the total current that can flow around the circuit. Using V=IR, an increase in current means a decrease in the total resistance of the circuit.
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REQUIRED PRACTICAL - Adding resistors in a series.

1) First, you'll need to find at least four identical resistors. 

2) Then, build a circuit connecting a resistor, battery and ammeter in series, making note of the pd of the battery.

3) Measure the current through the circuit using the ammeter, use this to calculate the resistance of the circuit, using R=V/I.

4) Add another resistor, in series with the first.

5) Again, measure the current and use this and the pd of the battery to calculate the overall resistance of the circuit.

6) Repeat steps 4 and 5, until you've added all of your resistors.

7) Plot a graph of the number of resistors against the total resistance of the circuit.

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REQUIRED PRACTICAL - Adding resistors in parallel.

1) Connect a resistor, a battery and an ammeter in series. Makes it a fair test.

2) Measure the total current through the circuit and calculate the resistance of the circuit using R=V/I, where V is the pd of the battery.

3) Next, add another resistor which is in parallel with the first.

4) Measure the total current through the circuit and use this and the pd of the battery to calculate the overall resistance of the circuit.

5) Repeat steps 3 and 4 until you've added all of your resistors.

6) Plot a graph of the number of resistors in the circuit against the total resistance.

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REQUIRED PRACTICAL - Results of parallel and serie

  • Should match the "resistance rules".
  • Adding the resistors in series increases the total resistance of the current (adding a resistor decreases the total current through the circuit).
  • The more resistors you add, the larger the resistance of the whole circuit. 
  • When you add resistors in parallel, the total current through the circuit increases - so the total resistance of the circuit has decreased.
  • The more resistors you add, the smaller the overall resistance becomes.
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What is the difference between AC and DC.

  • Mains supply is AC (alternating current) and battery supply is DC (direct current).
  • Mains electricity is an ac supply. In the United Kingdom the domestic electricity supply has a frequency of 50 Hz and is about 230 V.
  • In AC supplies, the current is constantly changing direction. They are produced by alternating potential difference in which the positive and negative ends keep alternating.
  • DC is a current that is always flowing in the same direction, and its created by a direct potential difference.
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Describe the three separate wires in most cables.

The insulation covering each wire is colour coded for easy identification:

  • live wire – brown. The live wire carries the alternating potential difference from the supply. 230 V.
  • neutral wire – blue. The neutral wire completes the circuit. 0 V.
  • earth wire – green and yellow stripes. The earth wire is a safety wire to stop the appliance becoming live. 0 V.

The potential difference between the live wire and earth (0 V) is about 230 V. The neutral wire is at, or close to, earth potential (0 V). The earth wire is at 0 V, it only carries a current if there is a fault.

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Why might the live wire may be dangerous?

  • a live wire may be dangerous even when a switch in the mains circuit is open.
  • your body, like the earth, is at 0 V.
  • this means that if you touch the live wire, a large potential difference is produced across your body and a current flows through you. 
  • this causes a large electric shock which could injure you or even kill you.
  • even if a plug socket or light switch is turned off, (ie. the switch is open) there is still a danger of an electric shock. A current isn't flowing, but there is still a pd in the live wire. 
  • if you made contact with the live wire, your body would provide a link between the supply and the earth, so a current would flow through you.
  • any connection between live and earth can be dangerous. If the link creates a low resistance path to earth, a huge current will flow, which could result in a fire.
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How is energy transferred?

  • Energy is transferred from cells and other sources.
  • A moving charge transfers energy because the charge does work against the resistance of the circuit and work done is the same as energy transferred.
  • Electrical appliances are designed to transfer energy to components in the circuit when a current flows.
  • Kettles transfer energy electrically from the mains AC supply to the thermal energy store of the heatig element inside the kettle. 
  • Energy is transferred electrically from the battery of a handheld fan to the kinetic energy store of the fan's motor.
  • No appliance transfers all of the energy completely usefully.
  • The higher the current, the more energy is transferred to the thermal energy stores of the components (and then to the surroundings).
  • Calculating the efficiency of any electrical appliance is possible.
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What is the equation for power, pd and current?

power = potential difference × current

OR

P = V I

  • power, P, in watts, W
  • potential difference, V, in volts, V
  • current, I, in amperes, A (amp is acceptable for ampere)
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What is the equation for power, current and resist

power = current²  × resistance

OR

P = I²R

  • power, P, in watts, W
  • current, I, in amperes, A (amp is acceptable for ampere)
  • resistance, R, in ohms, Ω
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What is the equation for energy transferred, power

energy transferred  = power × time

OR

E = P t

  • energy transferred, E, in joules, J
  • power, P, in watts, W
  • time, t, in seconds, s
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What is the equation for energy transferred, charg

energy transferred = charge flow  × potential difference

OR

E = Q V

  • energy transferred, E, in joules, J
  • charge flow, Q, in coulombs, C
  • potential difference, V, in volts, V
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What is pd?

  • Energy transferred per charge passed.
  • When an electrical charge goes through a change in pd, energy is transferred.
  • Energy is supplied to the charge at the power source to 'raise' it through a potential.
  • The charge gives up this energy when it 'falls' through any potential drop in components anywhere in the circuit. 
  • E=QV, a batter with a bigger pd will supply more energy to the circuit for every coulomb of charge which flows around it, because the charge is raised up "higher" at the start.
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How is electricity distributed?

  • Electrical power is transferred from power stations to consumers using the National Grid.
  • The National Grid is a system of cables and transformers linking power stations to consumers.
  • Step-up transformers are used to increase the potential difference from the power station to the transmission cables then step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use.
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Why does electricity production have to meet deman

  • Throughout the day, electricity usage (demand) changes.
  • Power stations have to produce enough electricity for everyone to have it when they need it.
  • They can predict when the most electricity will be used though. 
  • Demand increases when people get up in the morning, come home from school or work and when it starts to get dark or cold outside.
  • Popular events like a sporting final being shown on TV could also cause a peak in demand.
  • Power stations often run at well below their maximum power output, so there's spare capacity to cope with a high demand, even if there's an unexpected shut down of another station.
  • Lot's of smaller power stations that can start up quickly are also kept in standby just in case.
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How is the National Grid efficient?

  • Uses a high pd and a low current because of P=VI.
  • The problem with a high current is that you lose lots of energy as the wires heat up and energy is transferred to the thermal energy stores of the surroundings.
  • It's much cheaper to boost the pd up really high (to 400000 V) and keep the current relatively low.
  • For a given power, increasing the pd decreases the current, which decreases the energy lost by heating the wires and the surroundings. 
  • This makes an efficient way of transferring energy.
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How can pd be changed by a transformer?

  • To get the pd to 400000 V to transmit power requires transformers as well as big pylons with huge insulators - but it's still cheaper.
  • The transformers have to step the potential difference up at one end, for efficient transmission, and then bring it back down to safe, usable levels at the other end.
  • The potential difference is increased (stepped up) using a step up transformer.
  • The potential difference is decreased (stepped down) for domestic use using a step down transformer.
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Describe step up and step down transformers.

  • Step-up transformers have more turns on the secondary coil than they do on the primary coil.
  • Step-down transformers have fewer turns on the secondary coil than they do on the primary coil.
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How does static charge build up?

  • Through friction.
  • When certain insulating materials are rubbed against each other they become electrically charged.
  • Negatively charged electrons are rubbed off one material and on to the other.
  • The material that gains electrons becomes negatively charged.
  • The material that loses electrons is left with an equal positive charge.
  • Both positive (+ve) and negative (-ve) electrostatic charges are only ever produced by the movements of electrons. The positive charges DON'T move.
  • A positive static charge is always caused by electrons moving away elsewhere.
  • The material that loses the electrons loses some negative charge, and is left with an equal positive charge.
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Two electrically charged objects coming too close.

  • When two electrically charged objects are brought close together they exert a force on each other.
  • Two objects that carry the same type of charge repel.
  • Two objects that carry different types of charge attract.
  • Attraction and repulsion between two charged objects are examples of non-contact force.
  • These forces get weaker the further apart the two objects are.
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What happens when there is too much static?

  • Too much static causes sparks.
  • As electric charge builds on an object, the pd between the object and the earth (0 V) increases.
  • If the pd gets large enough, electrons can jump across the gap between the charged objects and the earth - this is the spark.
  • They can also jump to any earthed conductor that is nearby - which is why humans can get static shocks getting out of a car. A charge builds up on the car's metal frame and when you touch the car, the charge travels through you to earth.
  • This usually happens when the gap is fairly small.
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How to test if the forces cause the object to move

  • The forces can cause objects to move if they are able to do so, this is called electrostatic attraction/repulsion and is a non-contact force.
  • One way to see this is by suspending a rod with a known charge from a piece of string so that it is free to move.
  • Placing an object with the same charge nearby will repel the rod, causing the rod to move away from the object. 
  • An oppositely charged object will cause the rod to move towards the object.
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What do electric charges create?

  • An electric field is usually created around an electrically charged object.
  • The electric field is strongest close to the charged object.
  • The further away from the charged object, the weaker the field.
  • When drawing the field lines for an isolated (not interacting with anything), charged sphere remember that:
  • Electric field lines go from positive to negative.
  • They're always at a right angle to the surface.
  • The closer the lines are, the stronger the field is.
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What do charged objects in an electric field feel?

  • A second charged object placed in the field experiences a force.
  • The force causes the attraction or repulsion.
  • The force is caused by the electric fields of each charged object interacting with each other.
  • The force gets stronger as the distance between the objects decreases.
  • Two oppositely charged particles Q (+ve) and q (-ve):
  • The electric field of Q interacts with the electric field of q.
  • This causes forces to act on both Q and q.
  • These forces move q and Q closer together.
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How can sparking be explained through electric fie

  • Sparks are caused when there is a high enough potential difference between a charged object and the earth.
  • A high pd causes strong electric fields between the charged object and the earthed object.
  • The strong electric field causes electrons in the air particles to be removed - known as ionisation.
  • Air is normally an insulator, but when it is ionised, it is much more conductive, so a current can flow through it.
  • This is the spark.
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Describe the particle model of solids.

  • Strong forces of attraction hold the particles close together in a fixed, regular arrangement.
  • These particles don't have much energy so they can only vibrate about their fixed positions.
  • The density is generally highest in this state as the particles are closest together.
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Describe the particle model of 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.
  • For any given substance, in the liquid state its particles will have more energy than in the solid state (but less energy than in the gas state).
  • They move around in random directions at low speeds.
  • Liquids are generally less dense than solids.
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Describe the particle model of gases.

  • There are almost no force of attraction between the particles.
  • For any given substance, in the gas state its particles will have more energy than in the solid state or the liquid state.
  • They are free to move, and travel in random directions and at high speeds.
  • Gases have low densities.
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What is the equation for density?

density = mass volume

OR

ρ = m V

  • density, ρ, in kilograms per metre cubed, kg/m3
  • mass, m, in kilograms, kg
  • volume, V, in metres cubed, m3
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REQUIRED PRACTICAL - Density of a solid object.

1) Use a balance to measure its mass.

2) For regular solid shapes, the volume is simply worked out using a formula. For eg. the volume of a cube is just width x length x height.

3) For irregular shaped solids, you can work out its volume by submerging it into a eureka can filled with water. The water displaced by the object will be transferred to the measuring cylinder.

4) Record the volume of water in the measuring cylinder. This is the volume of the object.

5) Density = mass/volume.

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REQUIRED PRACTICAL - Density of a liquid.

1) Place a measuring cylinder on a balance and zero the balance.

2) Pour 10 ml of the liquid into the measuring cylinder and record the liquid's mass.

3) Pour another 10 ml into the measuring the cylinder and record the total volume and mass. Repeat this process until the measuring cylinder is full.

4) For each measurement, use Density = mass/volume to work out the density. 1 ml = 1 cubic cm.

5) Finally, take an average on your calculated densities to get an accurate value for the density of the liquid.

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What is internal energy?

  • Energy is stored inside a system by the particles (atoms and molecules) that make up the system. This is called internal energy.
  • Internal energy is the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system.
  • Heating changes the energy stored within the system by increasing the energy of the particles that make up the system. Heating the system transfers energy to its particles (they gain energy in their kinetic stores and move faster), increasing the internal energy.
  • This either raises the temperature of the system or produces a change of state. 
  • If the temperature changes, the size of the change depends on the mass of the substance it is made of (SHC) and the energy input. 
  • The change of state can be produced because if the substance is heated enough, the particles will have enough energy in their kinetic energy stores to break the bonds holding them together.
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What are changes of state?

  • Changes of state are physical changes which differ from chemical changes because the material recovers its original properties if the change is reversed.
  • Solid to liquid : Melting
  • Liquid to solid: Freezing
  • Solid to gas: Sublimating
  • Liquid to gas: Boiling/evaporating
  • Gas to liquid: Condensing
  • The number of particles doesn't change, they're just arranged differently, which means that mass is conserved, none of it is lost when the substance changes state.
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What does a change of state require?

  • A change of state requires energy.
  • When a substance is melting or boiling, you're still putting in energy and increasing the internal energy, but the energy's being used for breaking the intermolecular bonds rather than raising the temperature.
  • This causes flat spots on the heating graph where energy is being transferred by heating but not being used to change the temperature.
  • When a substance is condensing or freezing, bonds are forming between particles, which releases energy. 
  • This means that the internal energy decreases, but the temperature doesn't go down until all the substance has turned into liquid (condensing) or a solid (freezing).
  • The flat parts of the graph show this energy transfer.
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What is specific latent heat?

  • The specific latent heat of a substance is the amount of energy required to change the state of one kilogram of the substance with no change in temperature.
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When to use specific heat capacity formula.

  • If the temperature of the system increases, the increase in temperature depends on the mass of the substance heated, the type of material and the energy input to the system.
  • The following equation applies:
  • change in thermal energy  = mass  × specic heat capacity  × temperature change
  • ∆ E = m c ∆ θ
  • change in thermal energy, ∆E, in joules, J
  • mass, m, in kilograms, kg
  • specific heat capacity, c, in joules per kilogram per degree Celsius, J/kg °C
  • temperature change, ∆θ, in degrees Celsius, °C.
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What is the equation for specific latent heat?

energy for a change of state  = mass  × specific latent heat

OR

E = m L

  • energy, E, in joules, J
  • mass, m, in kilograms, kg
  • specific latent heat, L, in joules per kilogram, J/kg
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What is specific latent heat of fusion and vaporis

  • Specific latent heat of fusion – change of state from solid to liquid
  • Specific latent heat of vaporisation – change of state from liquid to vapour
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How can a gas be expanded or compressed?

  • A gas can be compressed or expanded by pressure changes.
  • The pressure produces a net force at right angles to the wall of the gas container (or any surface).
  • As gas particles move about high speeds, they collide into each other.
  • When they exert a force and a pressure on it.
  • In a sealed container, the outward gas pressure is the total force exerted by all of the particles in the gas on a unit area of the container walls.
  • Faster particles and more frequent collisions both lead to an increase in net force and gas pressure.
  • One way of increasing the speed of the particles is to heat them up. If volume is kept constant, then increasing the temperature will increase the speed of the particles, and so the pressure.
  • Alternatively, if temperature is constant, increasing the volume of a gas means the particles will get more spread out and hit the walls of the container less often which causes the gas pressure to decrease.
  • Pressure and volume are inversely proportional: at a constant temperature, when volume increases, pressure decreases. When volume decreases, pressure increases.
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What is the equation for pressure, volume and cons

pressure × volume  =  constant

OR

p V = constant

  • pressure, p, in pascals, Pa
  • volume, V, in metres cubed, m3
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What is average energy in kinetic stores related t

  • Average energy in kinetic stores is related to temperature.
  • The particles in a gas are constantly moving with random directions and speeds.
  • If you increase the temperature of a gas, you transfer energy into the kinetic energy stores of its particles.
  • The temperature of a gas is related to the average energy in the kinetic energy store of the particles in the gas.
  • The higher the temperature, the higher the average energy.
  • So as you increase the temperature of a gas, the average speed of its particles increases. This is because the energy in the particles' kinetic energy store is 1/2 x mass x (velocity)2 (squared).
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What can a change in pressure cause?

  • A change in pressure can cause a change in volume.
  • The pressure of a gas causes a net outwards force at right angles to the surface of its container.
  • There is also a force on the outside of the container due to the pressure of the gas around it.
  • If a container can easily change its size, like a balloon, then any change in these pressures will cause the container to compress or expand due to the overall force.
  • Eg. if a helium balloon is released, it rises. Atmospheric pressure decreases with height, so the pressure outside the balloon decreases. This causes the balloon to expand until the pressure inside drops to the same as the atmospheric pressure.
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What can doing work on a gas do?

  • Doing work on a gas can increase its temperature.
  • Work is the transfer of energy by a force. 
  • Doing work on a gas increases its internal energy, which can increase its temperature.
  • You can do work on a gas mechanically eg. with a bike pump. The gas applies pressure to the plunger of the pump and so exerts a force on it.
  • Work has to be done against this force to push down the plunger.
  • This transfers energy to the kinetic energy stores of the gas particles, increasing the temperature. If the pump is connected to a tyre, the tyre should start to become warmer.
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The nuclear model replaced the plum pudding model.

  • In 1834, John Dalton agreed that matter was made up of tiny spheres that couldn't be broken up, but he believed that each element was made up of a different type of these tiny spheres/atoms.
  • Nearly 100 years later, J.J. Thompson discoevered electrons that could be removed from atoms. This disproved Dalton's theory that atom's couldn't be split up. He suggested that atoms where spheres of positive charge with negative electrons embedded throughout: plum pudding model.
  • The results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was positively charged. From the plum pudding, they expected the particles to pass straight through the thin sheet of gold or only be slightly deflected. Although most did go through, more particles were deflected than previously thought. This nuclear model replaced the plum pudding model.
  • They also realised that because nearly all of the alpha particles passed straight through, most of the atom is just empty space. This was the first nuclear model of the atom.
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What did Bohr do?

  • He refined Rutherford's nuclear model.
  • Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances.
  • The theoretical calculations of Bohr agreed with experimental observations.
  • Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. The name proton was given to these particles.
  • Evidence from further experiments changed the model to have a nucleus made up of a group of particles (protons) which all had the same positive charge that added up to the overall charge of the nucleus.
  • About 20 years after the idea of the nucleus was adapted, in 1932, James Chadwick proved the existance of the neutron, which explained the imbalance between the atomic and mass numbers.
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What are isotopes?

Mass number: protons and neutrons.

Atomic number: protons, and protons = electrons. 

  • Isotopes of an element are atoms with the same number of protons but a different number of neutrons.
  • All elements have different isotopes, but there usually only one or two stable ones.
  • The other unstable isotopes tend to decay into other elements and give out radiation as they try to become stable. This process is called radioactive decay. (Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable. This is a random process called radioactive decay).
  • Radioactive substances split out one or more types of ionising radiation from their nucleus, like alpha, beta and gamma.
  • They can also release neutrons when they decay.
  • Ionising radiation is radiation that knocks electrons off atoms, creating positive ions. The ionising power of a radiation source is how easily it can do this.
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What is activity?

  • Activity is the rate at which a source of unstable nuclei decays, measured in becquerel (Bq).
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What is counter-rate?

  • Count-rate is the number of decays recorded each second by a detector (eg Geiger-Muller tube).
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Describe alpha particles.

  • an alpha particle (α) – this consists of two neutrons and two protons, it is the same as a helium nucleus.
  • they don't penetrate very far into materials and are stopped quickly - they only travel a few cm in air and are absorbed by a sheet of paper.
  • due to their size, they are strongly ionising.
  • at home, the can be used in smoke detectors - it ionises air particles, causing a current to flow. If there is smoke in the air, it binds to the ions, meaning the current stops and the alarm sounds.
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Describe beta particles.

  • a beta particle (β) – a high speed electron ejected from the nucleus as a neutron turns into a proton.
  • beta particles have no mass and have a charge of -1.
  • moderately ionising.
  • penetrate moderately far into materials before colliding and have a range in air of a few metres. They are absorbed by a sheet of aluminium which is around 5 mm thick. 
  • for every beta particle emitted, a neutron in the nucleus has turned into a proton.
  • can be used for: testing the thickness of sheets of metal, as the particles are not immediately absorbed by the material like alpha radiation would be and do not penetrate as far as gamma rays. Therefore, slight variations in thickness affect the amount of radiation passing through the sheet.
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Describe gamma rays.

  • a gamma ray (γ) – electromagnetic radiation from the nucleus.
  • they are EM waves with a short wavelength.
  • they penetrate far into materials without being stopped and will travel a long distance through the air.
  • they are weakly ionising because they tend to pass throguh rather than collide with atoms. Eventually they hit something and do damage.
  • can be absorbed by thick sheets of lead or metres of concrete.
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What are nuclear equations?

  • Nuclear equations are used to represent radioactive decay by using element symbols. 
  • They are written in the form: atom decay -> atom (s) after decay + radiation emitted.
  • The total mass and atomic number must be equal on both sides.
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Describe alpha decay.

  • Alpha decay decreases the charge and mass of the nucleus.
  • Alpha particles are made up of 2 protons and 2 neutrons.
  • When an atom emits an alpha particle, its mass number decreases by 4 and its atomic number decreases by 2.
  • A proton is positively charged and a neutron is neutral, so the charge of the nucleus decreases.
  • The nuclear equations involving alpha decay can be written using a helium nucleus.
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Describe beta decay.

  • Beta decay increases the charge of the nucleus.
  • When beta decay occurs, a neutron in the nucleus turns into a proton and releases a fast moving electron (the beta particle).
  • The number of protons in the nucleus has increased by 1, which increases the positive charge of the nucleus (the atomic number).
  • Before the nucleus has lost a neutron and gained a proton during beta decay, the mass of the nucleus doesn't change (protons and neutrons have the same mass).
  • They are written like this:
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Describe gamma radiation.

  • Gamma rays don't change the charge or mass of the nucleus.
  • Gamma rays are a way of getting rid of excess energy from a nucleus.
  • This means that there is no change in the atomic mass or atomic number of the atom.
  • They can be written:
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What is radioactivity?

  • Radioactive decay is random. This means that it is difficult to predict exactly which nucleus in a sample will decay next, or when any one of them will decay.
  • The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve, or the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.
  • Activity is measured in Bq.
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What is half life?

  • The half life is the time taken for the number of radioactive nuclei in an isotope to halve.
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How does the radioactivity of a source decrease?

  • Radioactivity of a source decreases over time.
  • Each time a radioactive nucleus decays to become a stable nucleus, the activity as a whole will decrease. (Older sources emit less radiation).
  • For some isotopes it takes just a few hours before nearly all of the unstable nuclei have decayed, whilst others last for millions of years.
  • The problem with trying to measure this is that the activity never reaches 0, which is why we have the idea of half-life to measure how quickly the activity drops off.
  • A short half-life means that the activity falls quickly, because the nuclei are very unstable and rapidly decay. Sources with a short-half life can be dangerous because of the high amount of radiation they emit at the start, but they quickly become safe.
  • A long half-life means that the activity falls more slowly, because most of the nuclei don't decay for a long time - the source just sits there, releasing small amounts of radiation for a long time. This can be dangerous because nearby areas are exposed to radiation for years.
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What is radioactive contamination?

  • Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials.
  • The hazard from contamination is due to the decay of the contaminating atoms.
  • The type of radiation emitted affects the level of hazard for example, the radioactie particles could get inside your body. 
  • Gloves and tongs should be used when handling sources, to avoid particles getting stuck to your skin or underneath your nails. 
  • Some industrial workers wear protective suits to stop them breathing in particles.
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What is irridation?

  • Irradiation is the process of exposing an object to nuclear radiation.
  • This simply means that they're exposed to it (we're always being irridated by background radiation sources).
  • The irradiated object does not become radioactive.
  • Keeping sources in lead-lined boxes, standing behind barriers or being in a different room and using remote controlled arms when working with radioactive sources are all ways of reducing irridation.
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What is background radiation?

  • Background radiation is the low level radiation that is around us all of the time.
  • It comes from:
  • natural sources such as rocks and cosmic rays from space. The cosmic rays are mostly from the sun, but the Earth's atmosphere protects us from them.
  • man-made sources such as the fallout from nuclear weapons testing and nuclear accidents. 
  • The level of background radiation and radiation dose may be affected by occupation and/or location.
  • Radiation dose is measured in sieverts (Sv) 1000 millisieverts (mSv) = 1 sievert (Sv).
  • The radiation dose tells you the risk of harm to body tissues due to exposure to radiation.
  • X-rays can affect levels of radiation.
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How can contamination and irridation cause harm?

  • Outside the body, beta and gamma sources are the most dangerous. This is because they can penetrate the body and get to delicate organs. Alpha is less dangerous becauseit can't penetrate the skin and is easily blocked by a small air gap. 
  • High levels of irridation from all sources are dangerous, especially from ones that emit beta and gamma.
  • Inside the body, alpha sources are the most dangerous, because they can do a lot of damage in a very localised area. So contamination rather than irridation is the major concern when working with alpha sources.
  • Beta sources are less damaging inside the body as radiation is absorbed oer a wider area, and some passes out of our body altogether. 
  • Gamma sources are the least dangerous inside the body as they mostly pass straight out - they have the lowest ionising power.
  • It is important for the findings of studies into the effects of radiation on humans to be published and shared with other scientists so that the findings can be checked by peer review.
  • Peer review can lead to improvements in our use of radioactive sources.
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What do radioactive isotopes have?

  • Radioactive isotopes have a very wide range of half-life values.
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How can nuclear radiation be used in medicine?

  • exploration of internal organs.
  • control or destruction of unwanted tissue.
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How are gamma rays used in medical tracers?

  • Certain radioactive isotopes can be injected into people (or they can swallow them) and their progress around the body can be followed using an external detector.
  • A computer converts the reading to a display showing where the strongest reading is coming from.
  • One example:
  • Iodine-123, which is absorbed by the thyroid gland (like normal idodine-127) but it gives out radiation which can be detected to indicate whether the thyroid gland is taking iodine as it should.
  • Isotopes which are taken into the body like this are usually gamma emitters (never alpha emitters), so that the radiation passes out of the body without causing much ionisation.
  • They should have a short half-life, so that the radioactivity inside the patient quickly disappears.
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Radiotherapy - treating cancer with radiation.

  • High doses of ionising radiation kills all living cells, it can be used to treat cancers.
  • Gamma rays are directed carefully and at the right dosage to kill the cancer cells without damaging too many normal cells.
  • Radiation-emitting implants (usually beta-emitters) can also be put next to or inside tumours.
  • However, a fair bit of damage is inevitably done to normal cells, which makes the patient feel very ill. 
  • But, if the cancer is killed off successfully in the end, then it would be worth it.
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What are the risks of using radiation?

  • Radiation can enter living cells and ionise atoms and molecules within them, can lead to tissue damage.
  • Lower doses tend to cause minor damage without klling the cells. This can give rise to mutant cells which divide uncontrollably. This is cancer.
  • Higher doses tend to kill cells completely, causing radiation sickness (leading to vomitting, tiredness and hair loss) if a lot of cells all get blasted at once.
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What are the benefits of using radiation?

  • Tracers can be used to diagnose life-threatening conditions, while the risk of cancer from the use of one tracer is very small.
  • Whilst prolonged exposure to radiation poses future risks and causes many side effects, many people with cancer chose to have radiotherapy as it may get rid of their cancer entirely. For them, the benefits outweigh the risks.
  • Perceived risk is how risky a person thinks something is. It's not the same as the actual risk of a procedure and the preceived risk can vary from person to person.
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Describe the process of nuclear fission.

  • It is the splitting of a large unstable nucleus, a type of nuclear reaction that is used to release energy from large and unstable atoms (eg. uranium or plutonium) by splitting them into smaller atoms.
  • Spontaneous (unforced) fission rarely happens. Uusally, the nucleus has to absorb a neutron before it will split.
  • When the atom splits, it forms two lighter elements that are roughly the same size (and have some energy in their kinetic energy stores).
  • Two or three neutrons 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 to occur. This is a chain reaction.
  • The energy not transferred to the kinetic energy stores of the products is carried away by gamma rays.
  • The energy carried away by the gamma rays, and in the kinetic energy stores of the remaining free neutrons and other decay products can be used to heat water, making steam to turn turbines and generators.
  • The amount of energy produced by fission in a nuclear reactor is controlled by chaning how quickly the chain reaction can occur. This is done using control rods like boron and silver, which when lowered and raised inside a nuclear reactor, absorbs neutrons. This slows down the chain reaction and controls the amount of energy released.
  • Uncontrolled chain reactions quickly lead to lots of energy being released as an explosion - this is how nuclear weapons work.
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Describe the process of nuclear fusion.

  • Opposite of nuclear fission.
  • Two light nuclei collide at high speed and join (fuse) to create a larger, heavier nucleus. For eg. hydrogen nuclei can fuse to produce a helium nucleus.
  • The heavier nucleus does not have as much mass as the two separate, light nuclei did. Some of the mass of the lighter nuclei is converted into energy. The energy is then released as radiation.
  • Fusion releases a lot of energy.
  • So far, scientists haven't found out a way of using fusion to generate energy for us to use. The temperatures and pressures needed to fusion are so high that fusion reactors are really hard and expensive to build.
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What is rectification?

  • AC electricity is supplied by the mains supply. DC electricity is supplied by batteries and solar cells. Many devices need a DC supply rather than an AC supply. A rectifier changes AC into DC. The process is called rectification and it uses diodes.
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What does a single diode produce?

  • A single diode can produce half-wave rectification. One half of the AC wave is removed because it cannot pass through the diode.A graph with the y axis both positive and negative. A wavy line half in the positive and half in the negative. It passes through a diode. Only the half of the wave in the positive remains because the other half cannot pass through the diode (http://www.bbc.co.uk/staticarchive/cb68d9c891790ea4f35edbeb8703e0f3cd9ef855.gif)
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Describe the process of controlled fission in nucl

  • Nucleus absorbs a neutron.
  • This causes the nucleus to split into two smaller nuclei.
  • In addition, energy is released as gamma radiation, as well as further neutrons are released.
  • These neutrons can then be absorbed by other nuclei and cause further fissions, triggering a chain reaction. 
  • The moderator slows down the neutrons to ensure that they are absorbed by the nuclei.
  • The control rods, absorb any additional neutrons, ensuring that the chain reaction is kept at a steady rate.
  • The control rods can be raised and lowered to maintain the chain reaction at a steady rate.
  • The energy released from the fission, can be used to heat water.
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Nuclear fission vs. Nuclear fusion.

  • In nuclear fusion, two light nuclei collide at high speeds and join (fuse) to create a larger, heavier nucleus.
  • Nuclear fusion two nuclei are pushed together hard enough that the nuclei fuse to form a heavier element. 
  • Some of the mass of the small nuclei is converted to energy.
  • This energy is then released as radiation.
  • Advantages: Fusion fuel readily available. No waste products. Fusion stops if plasma out of control.
  • Disadvantages: Large amounts of energy needed to start fusion. Plasma difficult to control. Currently fission produces more energy than fusion.
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What is black body radiation?

  • Radiation emitted by a body that absorbs all the radiation incident on it.
  • An object that has constant temperature emits radiation across a continuous range of wavelengths.
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