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Applied Single Award & Entry Level

WJEC Entry Level taught in conjunction with content from Applied Single Award Science to allow access to WJEC Double Award Science GCSE.

Applied Context It is important to understand energy transfer if we are to efficiently generate electricity or use energy in the home. Learners can apply their knowledge in a number of fields including electricity generation and sustainable development.

1.1.1 Underpinning Energy Concepts

Some of the tasks and questions that you are expected to complete will not be in this booklet.

You will need to bring the following to each of your lessons:

exercise book

pen, pencil, ruler, rubber and calculator.

Name: _______________________________________

Class: ________________________________________

Teacher: _____________________________________

Target Sheet: (dual) Applied Single Award & Entry Level WJECSingle Award = 1.1.1 Underpinning Energy Concepts

Subject Specific Targets Single Applied 1.1.1

BEFORE Unit

I have LEARNED

I understand how temperature differences lead to the transfer of energy.

Sankey diagrams to show energy transfers; energy efficiency in terms of input energy and energy usefully transferred in a range of contexts including electrical power generation, transmission and use of energy.

I am able to draw & interpret Sankey diagrams drawn to scale.

NB. On foundation tier, the equation will be given in the form required if it involves a change to the subject. I can use the following equations to find useful information relating to both the generation and use of electricity:

power = voltage current

e.g. in relation to the power output of wind turbines, water turbines and solar panels and power consumption of household appliances.

energy transfer = power time

I understand the relationship between watts and joules.

I know how to investigate energy transfer and the efficiency of energy transfer in a range of contexts; the interpretation, analysis and evaluation of data and methods used in investigations. Investigations to include:

the energy output from a renewable source (e.g. energy output and the construction / location of a wind turbine)

the efficiency of an electric kettle

I understand the terms sustainable and carbon footprint when applied to generation of electricity or the use of electricity and energy (e.g. natural gas).

I understand Carbon footprint as a measure of the total amount of carbon dioxide and methane emissions of a defined population, system or activity.

I am able to make a comparison of the carbon dioxide equivalent of greenhouse gases using given data.

I can use the measurement of the carbon footprint in terms of mass equivalent of carbon dioxide (kgCO2eq) and global warming potential of a gas; the use of the relationship:

kgCO2eq = (mass of a gas) (global warming potential of the gas)

It is important for us to understand energy transfer if we are to efficiently generate or use energy in the home. In this topic, we will aim to understand some key concepts which can then be applied to sustainable energy generation and use.

Forms of energy

You should be able to recognise the main forms of energy.

There are ten common energy types which need to be remembered. The easiest way to remember them is to make a word or phrase out of them.

The first letter of each word is the first letter of each energy type.

Lee - Eats - Hot - Soup - Most - Evenings - Kicking - Gravel - Not - Chippings.

Light

Electrical

Heat (thermal energy)

Sound

Magnetic

Elastic potential

Kinetic (movement energy)

Gravitational potential

Nuclear

Chemical.

The important thing to remember is:

energy is never created or destroyed

- it is only ever changed.

For example: in a battery-powered toy car, the chemical energy in the battery is changed into kinetic energy as the car moves.

Some energy changes are good (called useful energy changes). However, many energy changes are negative, called waste energy. Waste energy is a change that happens that we dont necessarily want. For example, televisions change electrical energy into light and sound (useful energy). However, they also produce heat energy that we dont need making the television get hot; this is wasted energy.

Useful

Useful

Wasted

Describe the energy changes in the following by drawing diagrams in your exercise book like the one above. In your diagram, show the useful energy and the wasted energy.

Q. What is the energy conversion in each of the solar cells?

Light

Q. What are the energy transfers in a wind turbine?

Q. What are the energy transfers in a hairdryer?

Efficiency

When we generate electricity or use energy in some way, the process will involve the transfer of energy. However not all of this energy is transferred usefully.

The efficiency of an energy transfer is the percentage of the energy transferred to useful energy output.

Whenever energy is transferred in a process, some energy is lost. For example if we generate electricity from coal only some of the energy stored in the coal is transferred to the electricity. The rest of the energy is wasted e.g. lost as heat energy to the surroundings.

For example:

In a coal-fired power station, only 400J was transferred to generate electricity for every 1000J of energy stored in coal. 600 J of energy was wasted as heat energy to the surroundings. We can use the equation below to calculate the efficiency of the process:

In a coal powered station chemical energy stored in coal is used to generate electricity. Not all that energy is converted into electricity. Some of the energy is lost to the surroundings as heat energy.

No machine is 100% efficient.

Think of 10 machines or appliances you use at home. How do they lose energy?

Activity: Which bulb is the most efficient?

1. Both lightbulbs will lose heat. (a) Which light bulb do you predict will lose the most heat (b) which lightbulb is the least efficient?

2. Draw a table to record the results of the above experiment.

3. Name the independent variable?

4. Name the dependent variable?

5. List all of the control variables:

6. How could you have improved the experiment?

7. You can show the energy conversions for a lightbulb by drawing a simple energy transfer diagram as below: How many joules of heat energy is wasted?

Electrical Energy 100J Light Energy (Useful) 60J

Heat Energy (Wasted) ? J

8. Copy this typical exam question and answer: What happens to the lost heat energy? Answer: Applying the principle of conservation of energy the wasted heat energy heats up the surroundings and becomes less useful.

Sankey Diagrams:

Captain Matthew Sankey developed Sankey diagrams as a clever way of illustrating both energy transfers & efficiency by drawing the width of the arrows to scale.

Sankey diagrams summarise all the energy transfers taking place in a process.

Activity:

What is the Sankey diagram of a filament bulb (below) telling you?

For every 10 J of electrical energy supplied to the lamp only 1J is transferred to the surroundings as light energy. The remainder, 9J (10J 1J) is transferred to the surroundings as heat energy.

We can draw Sankey diagrams for any process. Make sure you can draw a Sankey diagram and use a Sankey diagram to find information.

Top tips:

Useful energy is represented by the width of the horizontal arrows. You can think of this as the Wasted energy falls on the floor. (Exam questions and text books often get this wrong however!)

The WIDTH of the arrow must be drawn to scale (the length is not important).

Both Sankey diagrams below show:

The energy transferred from coal to electrical electricity (generated in a power station).

Sankey diagram showing efficiency as a %

Sankey diagram showing energy in joules (J)

Activity:

Draw both of the Sankey diagrams (below) to scale using graph paper or squared paper. Self-check them before showing them to a friend to check. Finally, glue them into your book and ask your teacher to check them. (Tip: use a pencil and ruler).

Task: Which lightbulb is the most efficient? How do you know?

Test yourself:

Q1.

Q2.

Energy transfer calculations

An electric current is the movement of a charge through an electrical conductor. When an electric current flows in a circuit, energy is transferred from the power supply to the components in the circuit.

Energy is measured in joules, J.

Power is measured in watts, W.

Power can be calculated using the equation:

P = V I

power (W) = potential difference (V) x current (A)

The amount of electrical energy transferred to an appliance depends upon the power rating of the appliance and the time for which it is switched on.

1 kW = 1000W

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