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
- 16 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 16
Watch first
Energy stores, transfers and efficiency
An English teaching video on this topic from BBC Bitesize - GCSE Revision Support. Watch it, then scroll down for the lesson.
In a nutshell
Calculate energy transfers and analyse electrical circuits at GCSE standard.
Learning cycle
Part 2 of 16
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 16
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.
Explore the idea
Part 4 of 16
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 5 of 16
Quick check
Kinetic energy is calculated as
Quick check
Part 6 of 16
Quick check
Efficiency equals
Reset break
Part 7 of 16
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.
Learning cycle
Part 8 of 16
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 9 of 16
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 10 of 16
Quick check
The National Grid transmits at high voltage to
Quick check
Part 11 of 16
Quick check
Wasted energy is
Explore the idea
Part 12 of 16
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 13 of 16
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
Challenge round
Part 14 of 16
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.
Mastery quiz
Part 15 of 16
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 16 of 16
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 LunaDo 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.
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
- Name the variable the club changed the second time, and one variable they kept the same.
- Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
- Write a conclusion for the club's report, saying how far the evidence supports it.
Method and results
WritingWrite 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
WritingExplain 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
DiagramDraw the apparatus or the process in pencil, label it fully, and photograph it.
1 labelled diagram
Reading and notes
ReadingRead 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 16 · Watch & discover