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
- 25 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 25
Visual introductionPicture this
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.
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
What you already know
Part 2 of 25
Before we start
What you already know
You should already know that energy is measured in joules and that machines waste energy as heat.
Key words
Part 3 of 25
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.
Reset break
Part 4 of 25
Pause
That's sitting 1 of 6 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.
Learning cycle
Part 5 of 25
Learning cycle 1 of 2
Stores and transfers
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 6 of 25
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.
Explore the idea
Part 7 of 25
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.
Reset break
Part 8 of 25
Pause
That's sitting 2 of 6 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.
Quick check
Part 9 of 25
Quick check
Part 10 of 25
Learning cycle
Part 11 of 25
Learning cycle 2 of 2
Dissipation and efficiency
A short piece of teaching, then a check to make sure it has landed.
Reset break
Part 12 of 25
Pause
That's sitting 3 of 6 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.
Explore the idea
Part 13 of 25
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.
Explore the idea
Part 14 of 25
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.
Quick check
Part 15 of 25
Reset break
Part 16 of 25
Pause
That's sitting 4 of 6 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.
Quick check
Part 17 of 25
Common mix-ups
Part 18 of 25
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.
Challenge round
Part 19 of 25
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
Reset break
Part 20 of 25
Pause
That's sitting 5 of 6 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.
Challenge round
Part 21 of 25
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
Total ____ before equals total energy after, always.
Challenge round
Part 22 of 25
Game · Recall cards
A stretched elastic band has energy in which store?
Card 1 of 4
Exit quiz
Part 23 of 25
Exit quiz
Show what you've learned
6 questions, marked together at the end. Nothing is timed.
1. Energy is measured in...
2. A falling ball transfers from...
3. Efficiency formula is...
4. Sankey arrow width shows...
5. Total energy after a change is...
6. Insulating a house mainly reduces...
Mastery quiz
Part 24 of 25
Marked quiz
End of lesson quiz: Energy stores, transfers and efficiency
4 questions, marked with the reasoning shown. No timer.
1. A stretched elastic band has energy in which store?
2. A lamp uses 60 J and emits 6 J of light. Efficiency is...
3. 'Wasted' energy has been...
4. Which is a transfer pathway?
Lesson round-up
Part 25 of 25
Lesson round-up
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Ask LunaPart 1 of 25 · Watch & discover