P8.2 - Powering Earth

Question 1

What are the differences between renewable and non-renewable energy?

Answer 1

Renewable energy can be produced and supplied at the rate it is being used and hence will not run out. However, non renewable sources of energy will eventually run out as they take a very long time to form and cannot be supplied at the rate they are being used up in.

Renewable energy sources such as solar and geothermal generate greenhouse gases do not generate greenhouse gases nor nuclear radiation.

Therefore, renewable energy sources don’t give rise to environmental problems such as global warming.

However, unlike non-renewable sources of energy, renewable sources of energy such as solar and wind, are unreliable.

Question 2

How do fossil fuel power plants work?

Answer 2

You burn fossil fuels such as coal, oil and gas.

The energy released heats water to make steam.

The steam turns a turbine.

The turbine turns a generator and electricity is produced.

Question 3

What is the difference between nuclear power plants and conventional power plants?

Answer 3

The heat required to turn the water to steam comes from nuclear fission reactions and not burning fossil fuels.

Question 4

What are the advantages and disadvantages of fossil fuels power plants?

Answer 4

Advantages

• Cost effective
• Reliable source of energy

Disadvantages

• The burning of fossil fuels releases greenhouses gases
• Fossil fuels are non-renewable

Question 5

What are the advantages and disadvantages of nuclear power plants?

Answer 5

Advantages

• Lots of energy per kg than fossil fuels
• No greenhouse gases produced

Disadvantages

• Radioactive waste is difficult to dispose of
• It is potentially very dangerous

Question 6

What are biofuels?

Answer 6

Biofuels are fuels that are obtained from living (or recently living) organisms.

Question 7

How are biofuels carbon neutral?

Answer 7

Biofuels are carbon neutral because the carbon dioxide released in burning biofuels is reabsorbed when a new crop of plants is grown.

This ensures that there is no net increase in the amount of carbon dioxide in the atmosphere.

Question 8

What are the two different types of ‘solar panels’?

Answer 8

Solar panels - Light energy to heat energy
Solar cells (photovoltaic cells) - Light energy to electrical energy

Question 9

What energy sources are used for heating?

Answer 9

• Fossil fuels
• Biofuels
• The sun
• Water pumped into hot rock

Question 10

What energy sources are used for transportation?

Answer 10

• Fossil fuels

- Biofuels

Question 11

What energy sources are used for generating energy?

Answer 11

• Fossil fuels
• Biofuels
• Nuclear fuel
• Solar power
• Tidal power
• Wind power
• Wave power
• Geothermal power
• Hydroelectric power

Question 12

Why has our use of energy sources changed over time?

Answer 12

There has been an increase in:

• Population
• The use of devices that use fuels
• Energy generation

Question 13

What do individuals or governments need to consider when deciding which energy sources to use?

Answer 13

Cost (to set up, and to remove)

Effect on the environment (pollution, how it looks if you live nearby)

Contribution to climate change.

How long the sources will last.

Question 14

What is The National Grid?

Answer 14

The National Grid is a network of cables and pylons, that transfer electrical energy generated in power plants to homes and businesses.

Question 15

Why are transformers used in the national grid?

Answer 15

The electricity has to be transferred over long distances. This electrical power can be subject to a lot of loss as heat, if the current is high.

Transformers are used to adjust the voltage (therefore the current) to minimise power/energy lost as heat.

Question 16

What is the purpose of step-up transformers?

Answer 16

Increase the voltage and hence decrease the current in the wires. This results in less energy lost as heat.

Question 17

What is the purpose of step-down transformers?

Answer 17

To decrease the voltage and hence increase the current in the wires. This results in appliances being able to be run at home without any problems.

Question 18

Why is electricity transferred through The National Grid at a much higher voltage than the voltage generated in a power station?

Answer 18

In order to reduce energy loss as heat.

Higher voltage results in each electron carrying more energy.

Subsequently there is a reduced current as this means that fewer electrons are needed to carry the energy which results in fewer collisions in the wire between the electrons and the wire atoms.

This in turn means that less heat energy is wasted.

Question 19

What is the transformer power equation?

Answer 19

Power in primary circuit = Power in secondary circuit

Current in primary circuit x Potential difference in primary circuit = Current in secondary circuit x Potential difference in secondary circuit

Question 20

Explain why the power lines supported by pylons have to be so high off the ground?

Answer 20

The power lines are at a high potential difference, with respect to the ground, and so there is high likelihood of current arching to the ground.

Question 21

What is the equation to calculate the efficiency of a transformer?

Answer 21

Efficiency of transformer = Power out (in secondary circuit) / Power in (in primary circuit)

Question 22

What is the domestic supply?

Answer 22

The electrical supply that we use in homes and businesses, which is AC and has a potential difference of 230V and 50Hz.

Question 23

What is the voltage for any appliance with a battery?

Answer 23

A direct voltage.

A potential difference that does not change direction.

Question 24

What does a UK plug have?

Answer 24

A UK plug has three pins which are connected to three different wires inside the socket in your wall.

Question 25

What does the live wires and neutral wires do in a plug?

Answer 25

The live wire (brown) and the neutral wire (blue) are two wires that make a complete circuit with the appliance.

Question 26

What does the earth wire do in a plug?

Answer 26

The earth wire (green and yellow) is not connected to the mains.

It is connected to the ‘earth’ which is usually a large metal pole buried in the ground outside your house.

Question 27

What happens if the live wire in an appliance becomes loose?

Answer 27

It can touch a metal casing, and we can say the casing is live.

If you touch the casing there is a potential difference of 230V across you because you are connected to the earth.

A dangerous current can flow through you.

Question 28

How is a dangerous current flowing through you when a live wire becomes loose prevented?

Answer 28

The earth wire connects the case to the pole in the ground so that current flows through the earth wire and not through you.

The earth wire has less resistance than you.

The wire inside the fuse also melts and switches of the circuit.

The appliances are also ‘double insulated’ (the wires and the plastic case) - So no current can flow through the case to you.