# OCR GCSE P3

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## Energy sources

A primary energy source is used in the form that it is found. For example, fossil fuels (coal, oil and gas), nuclear fuels, biofules from plants and animals, wind, waves and sunlight. Primary energy souces can transfer their energy to secondary energy sources. Most of our electricity is made from burning fossil fuels. Fossil fuels are non-renewable.

The burning of fossil fuels is increasing the amount of carbon dioxide, a greenhouse gas, in the atmosphere. The greenhouse effect is causing global warming, an increase in the temperature of the earth's surface. Global warming is likely to result in climate change, leading to floods and storms.

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## Power

Power is the amount of energy transferred in one second (the rate of energy transfer). A power of one watt transfers one joule of energy in one second. This is shown by the equation:

Energy transferred (kWh) = Power (kW) x Time (hrs)

The flow of electricity in a circuit is called current. It is measured in amperes. the voltage of a power supply is measured in volts. Electric current in an appliance transfers energy to it from the power supply. The rate at which this is done is found using the equation:

Electrical power (W) = Current (A) x Voltage (v)

The power of an electrical device is the rate at which it transfers energy from the power supply. This is usually given as a rating.

For an electrcial device of a given power rating, and an electricity supply of a given voltage, the current of the device needs to work is found using the equation:

Apliance current (A) + Appliance power (W) / Supply voltage (V)

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Current in a circuit results in both useful and unwanted energy transfers. Current in a component tranfers electrical energy into other useful forms. Current in the connecting wires wastefully transfers electrical energy into heat.

Electricity is measured in kWh or Units to keep the numbers manageable.

Electricty supplied to a component (Units) = Power (kW) x Time (hrs)

Cost of electricity = number of units supplied x cost per unit

Infromation about energy use can be displayed as:

• a pie chart to compare different uses of electricity
• a bar chart to show the amount of electricity used by different components
• a line graph to show how the number of units consumed changes with time
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## Sankey diagrams & efficiency

Sankey diagrams show the energy transfers in a component. In a Sankey diagram:

• Energy flows in from the left. The amount of energy input is shown at the left of the arrow tail and is proportional to the arrow tail's thickness.
• The sum of the widths of the new arrows is equal to the old arrow's width.
• Each energy output should be shown on the right with an arrow head. Useful energy transfers flow to the right and wasteful energy transfers flow downwards.

Theefficiency of a component tells you theproportion of energythat is transferred into a useful form.  Efficiency = energy usefully transferred / total energy supplied

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## Reducing energy levels

As a person, you can use less electricity by:

• using high efficiency A-rated appliances
• turning of components when they are not needed
• not boiling more water than is necessary

As a nation, we can use less energy by:

• using more efficient cars
• living in houses with better insulation
• building more efficient power stations and improving the output of old power stations

All human activity has an impact on the environment. This impact can be reduced by:

• recycling resources such as metals, glass and plastics
• generating electricity from renewable sources of energy eg. water, wind and solar power
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## Generators & how power stations work

Moving a magnet near a circuit causes an electric current to flow in the circuit. The current only flows when the magnetic field is changing and the magnet is moving.

Power stations use this idea to produce mains electricity by generators. A generator contains an electromagnet near a coil of wire. There is voltage across the coil when the electromagnet spins.

In thermal power stations, coal, oil, gas and nuclear power are used to spin the turbine from high pressure steam.

Hydroelectric power stations use a jet of high pressure water at the base of a dam to spin a turbine.

Wind-driven power stations use convection currents in the atmosphere caused by the heating effect of the sun on the land.

Nuclear power stations make high pressure steam by putting fuel rods close to each other in the reactor so that they heat up. Uranium atoms split releasing energy so fuel becomes hot. This heats the water turning it into steam.

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## Generators in power stations

1. Power stations use primary fuels such as fossil fuels, biofuels or nuclear fuels to boil water into steam.

2. The steam passes through a turbine, making it spin round.

3. The turbine spins the magnet inside the generator. Increasing the current drawn from the coil requires an increase in the rate of transfer of energy from the primary fuel.

4.The electricity produced goes to the transformers to produce the correct voltage.

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## Waste from power stations & risk

Waste from nuclear power stations is radioactive and is a serious health risk. Nuclear waste must be carefully stored until it becomes safe. Nuclear waste emits ionising radiation which affects body cells.

An object is only irradiated when it gets placed in the path of radiation. An object is contaminated when it gets mixed up with radioactive material. Contamination can be a more serious hazard than irradiation because it can result in longer exposure to radiation; it is difficult to remove the radioactive material.  It is also difficult to stop the radioactive material from spreading through the environment.

We often overestimate the risk from ionising radiation because:

• it cannot be seen or felt
• its effects take a long time to develop
• people worry about unfamiliar technology

Statistics about death rates can be used to compare risks from different technologies and decide which technologies need to be controlled. It also allows us to decide which risks are too small to worry about.

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• They can provide large amounts of electricity
• They can be turned on and off quickly
• They can pump water back behind the dam to store energy

• They flood large areas of land
• Rotting plants in the water produce methane gas
• They can cost a lot to build

• They are inexpensive to make
• They need very little maintenance

• They need to be put in windy places
• They can only generate electricity when there is enough wind
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## The National Grid

Electricity is convenient because it can transfer energy over long distances for many uses. The National Grid is a network of cables which carries electricity throughout the UK.

Power cables warm up because they wastefully transfer electrical current to thermal energy. Increasing the voltage of a power cable reduces the current. The National Grid carries electricity at a very high voltage to reduce wasteful energy transfers in the cables. Substations connected to the national grid reduce the voltage to 230V for out homes.

There are wasteful transfers of energy as it is generated and transmitted to the consumer. Wasteful energy transfers in transmission are much smaller than those in the power stations. The efficiency of electricity generation is the proportion of the energy in the original fuel that is delivered to the customer as electricity.

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## Choosing the best energy source

The energy sources that can produce large amounts of electricity are fossil fuels, nuclear power, biofuels and HEP. Energy sources that do not produce greenhouse gases are solar, wind, nuclear, waves and geothermal.

Some energy sources have environmental impacts:

• Fossil fuels produce greenhouse gases and extracting the fuels is dangerous and a pollution risk
• Nuclear power creates radioactive waste
• Wind farms can be noisy and cause visual pollution
• Hydroelectric and tidal dams flood large areas

When choosing an energy source, you should consider: its impact on the environment; the cost of building and running the power station; how much waste is produces; the reliability of the nergy source; the cost of using the enrgy source; the efficiency of the energy transfer.

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## Electricity choices in the future

The power output of a power station is measured in millions of watts or megawatts (MW). A power station that uses fossil or nuclear fuel has a steady output of about 1000MW and a lifetime of 40 years. Wind farms have a power output of 300 MW, although this varies with the weather, and a lifetime of about 20 years. HEP stations can have power outputs of about 10,000 MW with lifetimes of about 80 years.

In response to global warming, many countries have agreed to limit their production of carbon dioxide. They can do this by using less energy for transport, heating and electricity. Vehicles, factories and power stations emit less carbon dioxide if they become more efficient

Global demand for energy is likely to rise in the future because:

• there will be more people, especially in developing countries
• many of them want the high-energy lifestyle of an industralised country

Many goods imported by industralised countries are made in the developing world with polluting and inefficient technology. A secure energy supply in the future requires us to generate enough electricity to avoid power cuts but still have constant access to energy sources. We need to use more renewable enrgy sources in the future so that fossil fuels do not run out.

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