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Year 8

Conservation of Energy and Efficiency

Quantify energy, using box diagrams, and explain the idea of conservation of energy. Identify useful and wasted energy transfers and calculate efficiency from written questions and Sankey diagrams.

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Year 8

Conservation of Energy and Efficiency

Quantify energy, using box diagrams, and explain the idea of conservation of energy. Identify useful and wasted energy transfers and calculate efficiency from written questions and Sankey diagrams.

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Share activities with pupils

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Lesson details

Key learning points

  1. Describe energy transfers using box diagrams
  2. Apply the conservation of energy to examples
  3. Calculate the efficiency of energy transfers

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This content is made available by Oak National Academy Limited and its partners and licensed under Oak’s terms & conditions (Collection 1), except where otherwise stated.

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Starter quiz

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6 Questions

Q1.
What unit is energy measured in?
Correct answer: joules (J)
metres (m)
seconds (s)
watts (W)
Q2.
Which of these statements about energy is true?
Energy can be created.
Energy can be destroyed.
Correct answer: Energy can be transferred from one store to another.
Energy is only found in hot objects.
Q3.
A light bulb has energy transferred to it electrically. How is energy wasted by a light bulb?
Chemical energy is given out to the surroundings.
Gravitational potential energy is given out to the surroundings.
Nuclear energy is given out to the surroundings.
Correct answer: Thermal energy is given out to the surroundings.
Q4.
A washing machine transfers energy to its thermal and kinetic stores to wash clothes. How is energy wasted by a washing machine?
Chemical energy is given out to the surroundings.
Gravitational potential energy is given out to the surroundings.
Nuclear energy is given out to the surroundings.
Correct answer: Thermal energy is given out to the surroundings.
Q5.
Match the energy store to a real life example.
Correct Answer:kinetic energy,a football moving quickly

a football moving quickly

Correct Answer:gravitational potential energy,a book high up on a shelf

a book high up on a shelf

Correct Answer:chemical energy,a banana

a banana

Correct Answer:elastic potential energy,a bow pulled back to fire an arrow

a bow pulled back to fire an arrow

Q6.
Match the energy transfer to a real life example.
Correct Answer:electrical transfer,a circuit

a circuit

Correct Answer:mechanical transfer,a crane lifting an object

a crane lifting an object

Correct Answer:heating transfer,a frying pan warming up on a hob

a frying pan warming up on a hob

Correct Answer:radiation transfer,a microwave oven using microwaves to heat food

a microwave oven using microwaves to heat food

Exit quiz

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6 Questions

Q1.
What is the law of energy conservation?
Energy can be created and destroyed.
Energy can be created, but not destroyed.
Energy can be created, destroyed and transferred.
Correct answer: Energy cannot be created or destroyed, only transferred.
Q2.
What is energy dissipation?
when energy is transferred to many different stores
Correct answer: when energy is transferred to stores that are not useful
when energy is transferred to useful stores
Q3.
How is energy commonly dissipated?
by heating to the kinetic energy store of the surroundings
Correct answer: by heating to the thermal store of the surroundings
electrically to the kinetic energy store of the surroundings
mechanically to the thermal store of the surroundings
Q4.
How can efficiency be calculated?
efficiency = energy input ÷ useful energy output
efficiency = total energy output ÷ energy input
Correct answer: efficiency = useful energy output ÷ energy input
efficiency = useful energy output ÷ not useful energy output
Q5.
How is efficiency often shown?
as a fraction
Correct answer: as a percentage
in standard form
to the nearest 10
Q6.
What is the purpose of a Sankey diagram?
Correct answer: to show energy transfers in a system
to show the direction of energy transfers
to show the power in a system
to show the time taken for energy to transfer