Overview
You should be able to:
- Recognise different energy stores and describe how energy is transferred.
- Use the formulas E = P t, W = F s, GPE = m g h, KE = ½ m v² and efficiency = useful ÷ total.
- Describe conduction, convection and infrared radiation as ways of energy transfer.
- Explain how insulation reduces energy transfer from houses and other systems.
- Compare renewable and non-renewable energy resources: how they work, advantages and disadvantages.
Energy questions often link to other topics (forces, electricity, particles), so strong energy thinking helps across the whole paper.
1. Energy Stores & Transfers
Energy Stores
In the syllabus we usually talk about energy being stored in a small number of standard stores:
- Thermal (internal) – hot objects.
- Kinetic – moving objects.
- Gravitational potential – objects raised above the ground.
- Elastic potential – stretched or compressed springs and elastic bands.
- Chemical – fuels, food, batteries.
- Nuclear – energy in atomic nuclei.
- Electrostatic and magnetic – between separated charges or magnets.
Important idea: energy is conserved. It is never created or destroyed, only transferred between stores.
Ways Energy Is Transferred
Energy can be transferred by:
- Heating (conduction, convection, radiation).
- Mechanically (forces doing work – pushing, stretching, turning).
- Electrically (charges moving in a circuit).
- Radiation (light, infrared, sound waves, etc.).
Quick Check
Q1. A battery powers a motor that lifts a weight. Name two energy stores at the start and two at the end.
Show answer
Start: chemical energy in battery, some thermal in surroundings.
End: gravitational potential energy of lifted weight, thermal energy in motor/surroundings.
2. Work Done, GPE & Kinetic Energy
Work Done
When a force moves an object, energy is transferred and we say work is done.
W = F s
Unit of work / energy: joule (J).
F in newtons (N), s in metres (m).
Gravitational Potential Energy (GPE)
ΔEg = m g h
On Earth, g ≈ 9.8 N/kg – in IGCSE you can usually use 10 N/kg unless the question says otherwise.
Kinetic Energy
Ek = ½ m v²
m in kg, v in m/s, energy in J.
Power
Power is the rate of energy transfer:
P = E / t
Unit of power: watt (W) = 1 J/s.
Quick Check
Q2. A 5 kg box is lifted 2.0 m. Take g = 10 N/kg. How much GPE does it gain?
Show answer
ΔE = m g h = 5 × 10 × 2.0 = 100 J.
Q3. A 1 000 kg car moves at 20 m/s. Calculate its kinetic energy.
Show answer
E = ½ m v² = 0.5 × 1 000 × 20² = 0.5 × 1 000 × 400 = 200 000 J.
3. Energy Transfer by Heating
Conduction
- Occurs mainly in solids.
- Particles in the hot part vibrate more and pass energy to neighbours.
- Metals are good conductors because of free electrons carrying energy quickly.
- Materials that do not conduct well are called insulators (e.g. wood, plastic, air).
Convection
- Occurs in liquids and gases.
- Warmer regions become less dense and rise; cooler, denser regions sink.
- This movement of the fluid forms a convection current that transfers energy.
Infrared Radiation
- All objects emit infrared (IR) radiation – hotter objects emit more.
- Does not need particles: can travel through a vacuum.
- Dark, matt surfaces are better absorbers and emitters than light, shiny surfaces.
In the exam you may be asked how different materials or designs reduce heat loss – always link to conduction, convection or radiation.
4. Insulation & Efficiency
Reducing Unwanted Energy Transfer
Examples around a house:
- Cavity wall insulation – trapped air / foam reduces conduction and convection.
- Loft insulation – fibre/foam reduces conduction through roof and convection in loft.
- Double glazing – two glass layers with air gap reduce conduction and convection.
- Draught excluders – reduce convection currents around doors and windows.
- Shiny foil behind radiators – reflects infrared radiation back into the room.
Efficiency
No device is 100% efficient: some input energy is always transferred to less useful stores (usually thermal in surroundings).
Quick Check
Q4. A lamp receives 200 J of electrical energy and transfers 40 J as light. What is its efficiency?
Show answer
efficiency = 40 / 200 = 0.20 → 20%.
5. Energy Resources
Non-renewable Resources
These will run out eventually and usually release greenhouse gases or radioactive waste.
- Fossil fuels – coal, oil, natural gas.
- Advantages: reliable, high energy output, existing power stations.
- Disadvantages: CO₂ emissions (global warming), sulfur dioxide (acid rain), limited reserves.
- Nuclear fuel (uranium / plutonium).
- Advantages: very high energy per kg, no CO₂ during operation.
- Disadvantages: radioactive waste, expensive to build/decommission, risk of accidents.
Renewable Resources
These are replaced naturally and will not run out on human time scales.
- Solar – solar panels or solar cells (PV) capture sunlight.
- Wind – turbines driven by moving air.
- Hydroelectric – water stored in dams flows through turbines.
- Tidal – turbines driven by tides in estuaries/barrages.
- Wave – machines use up-and-down motion of sea waves.
- Geothermal – hot rocks heat water to drive turbines.
- Biomass – plant material burned or used for biofuels.
Most renewables are variable (depend on weather/time of day) and need backup or storage.
Comparing Resources (Exam-style Phrases)
- Reliability: fossil and nuclear give constant output; wind and solar are not reliable on their own.
- Start-up time: gas is quick; nuclear and coal are slow.
- Environmental impact: fossil fuels → greenhouse gases; nuclear → long-term waste; renewables → visual/noise impact, land use, effects on habitats.
- Running cost vs set-up cost: fossil plants cheap to build but fuel costs; many renewables expensive to build but cheap to run.
Quick Check
Q5. Give one advantage and one disadvantage of wind power compared with coal.
Show answer
Advantage: no fuel cost and no CO₂ during operation.
Disadvantage: output is variable (depends on wind) and large numbers of turbines are needed.
What Next?
To finish this topic strongly:
- Practise calculations with W = F s, GPE = m g h, KE = ½ m v², P = E / t and efficiency.
- Draw and label at least one Sankey diagram on your own.
- Make a table comparing all major energy resources: how they work, pros and cons.
- Do past-paper questions on energy transfer in houses, power stations and everyday devices.