Energy Transfer
Module Overview & Key Units
Learning Outcomes
- 4.1 Use the following units: kilogram (kg), joule (J), metre (m), metre/second (m/s), metre/second² (m/s²), newton (N), second (s) and watt (W).
This module explores how energy is stored and transferred, the fundamental principle of energy conservation, the concept of efficiency, and the mechanisms of thermal energy transfer.
1. Energy Stores and Transfers
Learning Outcomes (4.2, 4.5)
- Describe energy transfers involving the 8 energy stores and 4 transfer pathways.
- Describe everyday devices, explaining the transfer of input energy.
Energy is never created or destroyed, but it can be stored in different ways and transferred between stores.
Energy Stores
Energy Transfers
- Mechanically — a force does work (pushing, lifting)
- Electrically — charges flow through a circuit
- By Heating — temperature difference drives energy flow
- By Radiation — energy as waves (light, sound)
Example: A Bouncing Ball
- Ball held high → Gravitational PE store
- Falls: GPE decreases, KE increases (mechanical transfer); some to thermal (air resistance)
- Hits ground: KE → Elastic PE + Thermal + Sound
- Bounces up: Elastic PE → KE → GPE
Example: Battery-Powered Torch
- Battery: Chemical energy store
- Switched on: Chemical energy transferred electrically to bulb
- Bulb: Electrical → Light (useful, radiation) + Heat (wasted, heating)
Simulation: Bouncing Ball Energy Transfer
Watch how energy transfers between GPE, KE, and Thermal stores as a ball bounces.
2. Conservation of Energy
Learning Outcome (4.3)
- Use the principle of conservation of energy.
The total energy in a closed system remains constant. Energy can change forms, but the sum of all energy stays the same.
Simulation: Pendulum — GPE & KE Transfer
See how gravitational PE converts to kinetic energy and back. Toggle friction to observe energy dissipation.
3. Efficiency & Sankey Diagrams
Learning Outcomes (4.4, 4.5)
- Know and use: Efficiency = (Useful Energy Output / Total Energy Input) × 100%
- Represent energy transfers using Sankey diagrams.
No device is 100% efficient; some energy is always dissipated, typically as heat.
Efficiency Calculator
Sankey Diagram
The widths of the arrows are proportional to the energy amounts.
4. Thermal Energy Transfer
Learning Outcomes (4.6–4.8, 4.10)
- Describe thermal energy transfer by conduction, convection and radiation.
- Explain the role of convection in everyday phenomena.
- Explain how emission/absorption relate to surface and temperature.
- Explain ways of reducing unwanted energy transfer.
A. Conduction
Conduction transfers thermal energy through a substance without the substance moving. It mainly occurs in solids. Heated particles vibrate more vigorously, passing energy to neighbours. In metals, free electrons also carry energy rapidly.
💡 A metal spoon in hot tea — the handle becomes hot because energy is conducted along the metal.
Good conductors: metals. Poor conductors (insulators): wood, plastic, air.
Simulation: Conduction Race
Compare how fast heat travels through different materials. Watch the colour change from blue (cold) to red (hot).
B. Convection
Convection transfers thermal energy in fluids (liquids and gases) by the movement of the fluid itself. Heated fluid expands, becomes less dense, and rises. Cooler fluid sinks, creating convection currents.
Everyday examples:
- Heating water in a kettle — element heats nearby water which rises
- Room heaters — warm air rises, cool air replaces it
- Sea & land breezes — differential heating of land and sea
C. Radiation
Radiation transfers thermal energy as infrared electromagnetic waves. It doesn't require a medium and works through a vacuum (e.g., sunlight reaching Earth).
- Dark, matt surfaces — good emitters & absorbers
- Light, shiny surfaces — poor emitters & absorbers (good reflectors)
- Hotter objects emit more radiation per second.
Simulation: Radiation Absorption Comparison
Compare how fast a dark matt surface and a shiny silver surface absorb infrared radiation.
D. Reducing Unwanted Energy Transfer
Insulation reduces the rate of unwanted thermal energy transfer.
| Method | How It Works | Example |
|---|---|---|
| Trapped Air | Air is a poor conductor; trapping it reduces conduction & convection | Loft insulation, cavity wall foam, double glazing |
| Reflective Surfaces | Shiny surfaces reflect infrared radiation back | Foil behind radiators, emergency blankets |
| Vacuum | No particles = no conduction or convection | Vacuum flask (Thermos) |
5. Practical Investigations
Learning Outcome (4.9)
- Investigate thermal energy transfer by conduction, convection and radiation.
Practical investigations are key to understanding thermal energy transfer. Below are typical setups with diagrams.
Investigating Conduction
Method: Attach pins with wax to rods of different materials. Heat one end equally. Record when each pin falls. Copper conducts fastest, glass slowest.
Investigating Convection in Liquids
Observation: Purple dye from potassium permanganate is carried upward by the warm rising water, showing the convection current path.
Investigating Convection in Gases
Observation: Smoke is drawn down the cold chimney, across the box, and up past the candle, making the convection current visible.
Investigating Radiation Emission (Leslie's Cube)
Investigating Radiation Absorption
6. Knowledge Check
1. Which of these is primarily a store of chemical energy?
2. A device uses 500 J of electrical energy and produces 350 J of useful light energy. What is its efficiency?
3. Which thermal energy transfer method is primarily responsible for the sun's energy reaching Earth?
4. A matt black surface is a good...
5. The principle of conservation of energy states that: