Calculating efficiency (in terms of useful energy transferred)
Lesson details
Learning outcome
I can calculate the efficiency of an energy transfer and describe ways in which energy is dissipated.
Key learning points
- Energy is dissipated due to friction which causes particles to vibrate more quickly and heats up the surroundings.
- Energy is dissipated due to drag which causes particles in the surroundings to move more quickly.
- Efficiency = (useful energy transferred by the device)/(total energy supplied to the device)
- Efficiency can be increased by lubrication, bearings or wheels.
Keywords
Dissipate - Friction can cause energy to dissipate (spread out and become unusable) into the surroundings, causing them to heat up.
Efficiency - Efficiency is the fraction of energy supplied to an object or system that is usefully transferred by it.
Useful energy transferred - The amount of energy usefully transferred by an object or system is the useful energy transferred by the device.
Total energy supplied - The total amount of energy transferred to an object or system is the total energy supplied to the device.
Common misconception
Pupils may not realise that energy transfers usually result in the heating of the surroundings and therefore some energy ends up in a thermal store.
Pupils should have opportunity to identify and describe places in a system where energy is dissipated and transferred into a thermal store.
Teacher tip
The practical activity in this lesson allows pupils to investigate and describe an example in which energy is dissipated in order to help develop understanding of ideas about efficiency. The activity is also useful for providing practice of measurement techniques and control variables.
Equipment
A selection of balls that bounce, a metre ruler, masking tape.
Content guidance
Risk assessment required - equipment
Supervision
Adult supervision required
Licence
except where otherwise stated. See Oak's terms & conditions (Collection 2).Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Which of the following energy stores does friction transfer energy into?
Q2.Why does a hot cup of tea cool down?
Q3.Why is the rebound height of a ball not the same as the height that it was dropped from?
Q4.The law of conservation of energy states that energy cannot be created or ...
Q5.Match the values on the left to the equivalent values on the right.
1500 W
3.4 kJ
340 J
0.015 kW
Q6.Which of the following statements explains why an electric heater can be considered to be 100% efficient?
Assessment exit quiz
6 Questions
Q1.Energy is when it is transferred to the thermal store of the surroundings.
Q2.Which of the following is a correct definition for efficiency?
Q3.Which of the following equations show the correct relationship between efficiency, useful output energy transfer and total input energy transfer?
Q4.A forklift truck transfers 24 000 J of energy when lifting a box onto a high shelf.
Calculate the efficiency of the truck if 18 000 J of energy is transferred to the gravitational store.
Q5.Aisha is investigating how the temperature of a tennis ball affects its rebound height.
Which of the following are control variables for this experiment?
Q6.An elevator has an efficiency of 0.8. When it lifts four people to the tenth floor, it uses 160 000 J of energy.
How much energy is transferred to the people?
To help you plan your 10 combined science lesson on: Calculating efficiency (in terms of useful energy transferred), download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 10 combined science lesson on: Calculating efficiency (in terms of useful energy transferred), download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 4 combined science lessons from the Energy of moving objects unit, dive into the full secondary combined science curriculum, or learn more about lesson planning.