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SavannahYear 8
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SciencePhysics foundations for GCSE (AQA 8463)30 min★★★ difficulty

Energy stores, transfers and efficiency

Energy is not used up. Describing it as stores and transfers, rather than 'types', is what makes GCSE physics calculations make sense.

Lesson overview

What you'll learn in this lesson

Understand energy as a quantity that can be quantified and calculated, and the total energy has the same value before and after a change

Key learning points

  • • Stores, not types
  • • Transfer pathways
  • • Conservation and dissipation
  • • Calculating efficiency

This lesson at a glance

  • 30 minutes
  • 19 parts to scroll through
  • 4 quick checks
  • Marked quiz at the end
  • Gentle pace: short sittings with pauses

Words to know

energyquantityquantifiedcalculatedbefore

Scroll down — the lesson carries on below

Part 1 of 19 · Discover5%
1

Watch & discover

Part 1 of 19

Watch first

Energy stores, transfers and efficiency

An English teaching video on this topic from GCSE Physics Explained. Watch it, then scroll down for the lesson.

In a nutshell

Understand energy as a quantity that can be quantified and calculated, and the total energy has the same value before and after a change

2

What you already know

Part 2 of 19

Before we start

What you already know

You should already know that energy is measured in joules and that machines waste energy as heat.

3

Key words

Part 3 of 19

Key words

Words you'll need today

Store
Where energy is at a moment: kinetic, thermal, chemical, elastic, gravitational.
Transfer
How energy moves: mechanically, electrically, by heating or by radiation.
Dissipation
Energy spreading to the surroundings, becoming less useful.
Efficiency
Useful energy output divided by total energy input.
Sankey diagram
A diagram whose arrow widths show energy transfers to scale.
4

Learning cycle

Part 4 of 19

Learning cycle 1 of 2

Stores and transfers

A short piece of teaching, then a check to make sure it has landed.

5

Explore the idea

Part 5 of 19

Learn

Stores, not types

A moving ball has a kinetic store; a stretched band an elastic store; a battery a chemical store. Ask two questions of any change: which store fell, and which rose? That question survives all the way through GCSE and A level.

6

Explore the idea

Part 6 of 19

Learn

Transfer pathways

The four pathways are mechanical (a force moving), electrical (a current flowing), heating, and radiation. A kettle transfers electrically from the mains to the thermal store of the water — and, unhelpfully, to the thermal store of the kitchen.

7

Quick check

Part 7 of 19

Quick check

A stretched elastic band has energy in which store?

8

Quick check

Part 8 of 19

Quick check

A lamp uses 60 J and emits 6 J of light. Efficiency is...

9

Reset break

Part 9 of 19

Pause

That's sitting 1 of 2 done

Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.

Stop here for now
10

Learning cycle

Part 10 of 19

Learning cycle 2 of 2

Dissipation and efficiency

A short piece of teaching, then a check to make sure it has landed.

11

Explore the idea

Part 11 of 19

Learn

Conservation and dissipation

Total energy before equals total energy after, always. But energy that spreads out into the surroundings is dissipated: still there, no longer useful. 'Wasted' means dispersed, not destroyed — a distinction examiners test constantly.

12

Explore the idea

Part 12 of 19

Learn

Calculating efficiency

Efficiency = useful output ÷ total input, as a decimal or percentage. A lamp taking 60 J and giving 6 J of light is 10% efficient; the other 54 J heats the room. Efficiency can never exceed 100%, so an answer above that means a mistake, not a discovery.

13

Quick check

Part 13 of 19

Quick check

'Wasted' energy has been...

14

Quick check

Part 14 of 19

Quick check

Which is a transfer pathway?

15

Common mix-ups

Part 15 of 19

Common mix-ups

Things people often get wrong

  • Energy is never used up or created — it is transferred and often dissipated.
  • Heat is a transfer, not a store; the store is thermal.
  • Efficiency above 100% is always an arithmetic error.
16

Challenge round

Part 16 of 19

Game · Sort it

Which of these are true?

Drag each card into the right column. Tap a card first if dragging is fiddly.

True

Not true

17

Challenge round

Part 17 of 19

Game · Fill the gaps

Finish the sentences

Choose the word that belongs in each gap.

Total ____ before equals total energy after, always.

18

Mastery quiz

Part 18 of 19

Marked quiz

End of lesson quiz: Energy stores, transfers and efficiency

6 questions, marked with the reasoning shown. No timer.

  1. 1. Energy is measured in...

  2. 2. A falling ball transfers from...

  3. 3. Efficiency formula is...

  4. 4. Sankey arrow width shows...

  5. 5. Total energy after a change is...

  6. 6. Insulating a house mainly reduces...

19

Lesson round-up

Part 19 of 19

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

0

Best run

0 in a row

Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?

Ask Luna

Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Case study

Why the school greenhouse failed

A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.

The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.

The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.

Written for Good Learning Co.

Reading questions

  1. Name the variable the club changed the second time, and one variable they kept the same.
  2. Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
  3. Write a conclusion for the club's report, saying how far the evidence supports it.

  • Method and results

    Writing

    Write the aim, what you changed, what you measured and what you kept the same, then record your results in a table.

    1 page + results table

  • Conclusion

    Writing

    Explain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.

    6–8 sentences

  • Labelled diagram

    Diagram

    Draw the apparatus or the process in pencil, label it fully, and photograph it.

    1 labelled diagram

  • Reading and notes

    Reading

    Read the lesson text again and write the key ideas in your own words.

    Half a page of notes

Saved as you type.

Part 1 of 19 · Watch & discover

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