Energy stores, transfers and efficiency
Physics answers about energy must name the store, the pathway and the destination. Vague answers about energy 'being used up' score nothing.
Lesson overview
What you'll learn in this lesson
Calculate energy transfers and analyse electrical circuits at GCSE standard.
Key learning points
- • Stores and calculations
- • Efficiency and dissipation
- • Power and national supply
This lesson at a glance
- 30 minutes
- 20 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 20
Visual introductionPicture this
Energy stores, transfers and efficiency
Physics answers about energy must name the store, the pathway and the destination. Vague answers about energy 'being used up' score nothing.
In a nutshell
Calculate energy transfers and analyse electrical circuits at GCSE standard.
Learning cycle
Part 2 of 20
Learning cycle 1 of 2
Part 1 · Stores and calculations
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 20
Learn
Stores and calculations
Kinetic energy = ½mv², gravitational potential energy = mgh and elastic potential energy = ½ke². Specific heat capacity questions use E = mcΔθ. Choosing the right equation depends on identifying which store is changing, so start every answer by naming it.
Reset break
Part 4 of 20
Pause
That's sitting 1 of 5 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 5 of 20
Learn
Efficiency and dissipation
Efficiency = useful output ÷ total input, as a decimal or percentage. Wasted energy is dissipated to the surroundings, usually by heating, and becomes too spread out to be useful. Lubrication, insulation and streamlining reduce these losses in specific, describable ways.
Quick check
Part 6 of 20
Quick check
Part 7 of 20
Reset break
Part 8 of 20
Pause
That's sitting 2 of 5 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 9 of 20
Learning cycle 2 of 2
Part 2 · Power and national supply
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 20
Learn
Power and national supply
Power = energy ÷ time, and for electricity P = IV or P = I²R. The National Grid uses transformers to raise the voltage and reduce the current for transmission, because power lost as heat depends on the square of the current, making high-voltage transmission far more efficient.
Quick check
Part 11 of 20
Reset break
Part 12 of 20
Pause
That's sitting 3 of 5 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 13 of 20
Explore the idea
Part 14 of 20
Worked example
Worked answer: a 60 kg cyclist accelerates from rest to 8 m/s. Find the kinetic energy gained (3 marks)
Kinetic energy = ½mv² (1). Substituting: ½ × 60 × 8² = ½ × 60 × 64 (1) = 1,920 J (1). The energy comes from the chemical store in the cyclist's muscles, transferred mechanically. Forgetting to square the speed gives 240 J, the most frequent error in this calculation.
Challenge round
Part 15 of 20
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 16 of 20
Pause
That's sitting 4 of 5 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 17 of 20
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
Kinetic ____ = ½mv², gravitational potential energy = mgh and elastic potential energy = ½ke².
Challenge round
Part 18 of 20
Game · Recall cards
Kinetic energy is calculated as
Card 1 of 4
Mastery quiz
Part 19 of 20
Marked quiz
End of lesson quiz: Energy stores, transfers and efficiency
4 questions, marked with the reasoning shown. No timer.
1. Kinetic energy is calculated as
2. Efficiency equals
3. The National Grid transmits at high voltage to
4. Wasted energy is
Lesson round-up
Part 20 of 20
Lesson round-up
Ready when you are
Quiz score
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Games
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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 LunaPart 1 of 20 · Watch & discover