Describe how energy is transferred between stores during events and processes, including examples of transfer by forces (mechanical work done), electrical currents (electrical work done), heating, and by electromagnetic, sound and other waves
Energy can be stored in many forms (stores) such as kinetic, gravitational, elastic, chemical, electrical, thermal, radiant, and sound. During an event or process, energy is transferred from one store to another. The transfer occurs through specific mechanisms, each described below with examples relevant to the Cambridge IGCSE syllabus.
1. Mechanical Work Done (Transfer by Forces)
When a force acts through a distance, work is done and energy is transferred between the kinetic, gravitational, and elastic stores.
Work done, \$W = F \times d \times \cos\theta\$ (Joules)
Example: Lifting a book onto a shelf – chemical energy in muscles → gravitational potential energy of the book.
Example: Compressing a spring – mechanical work → elastic potential energy.
Example: Pushing a sled on level ground – chemical energy → kinetic energy of the sled.
2. Electrical Work Done (Transfer by Electrical Currents)
Electrical energy is transferred when a charge moves through a potential difference.
Electrical work, \$W = V \times Q\$ where \$V\$ is voltage (V) and \$Q\$ is charge (C).
Power, \$P = V I\$ where \$I\$ is current (A).
Example: A battery powering a torch – chemical energy in the battery → electrical energy → light (radiant) and heat (thermal) energy.
Example: An electric heater – electrical energy → thermal energy.
3. Heating (Transfer by Temperature Difference)
Energy transfer as heat occurs when there is a temperature gradient.
Heat transferred, \$Q = m c \Delta T\$ where \$m\$ is mass, \$c\$ specific heat capacity, \$\Delta T\$ temperature change.
Example: Boiling water on a stove – electrical or chemical energy → thermal energy of water.
Example: Conduction through a metal rod – thermal energy moves from hot end to cold end.
4. Electromagnetic Waves (Radiant Energy Transfer)
Energy is carried by electromagnetic radiation and can be absorbed, reflected or transmitted.
Energy flux, \$I = \frac{P}{A}\$ where \$P\$ is power and \$A\$ is area.
Example: Sunlight warming the Earth – radiant energy → thermal energy.
Example: A microwave oven – electromagnetic waves → thermal energy in food.
5. Sound Waves (Acoustic Energy Transfer)
Sound waves transmit energy through the vibration of particles in a medium.
Intensity of sound, \$I = \frac{P}{A}\$ (same form as electromagnetic).
Example: A loudspeaker – electrical energy → sound energy → may be partially converted to thermal energy in the air.
Example: Echo in a canyon – sound energy reflected back to the source.
6. Other Wave Types (e.g., Water Waves)
Energy can also be transferred by mechanical waves in fluids.
Example: Ocean waves – wind energy → kinetic and potential energy of water particles → can be harnessed as electrical energy (tidal generators).
Example: Seismic waves – elastic energy in the Earth’s crust → can cause heating and mechanical damage.
Summary Table of Energy Transfer Mechanisms
Transfer Mechanism
Typical Energy Stores Involved
Representative Example (IGCSE Context)
Mechanical work (forces)
Kinetic ↔ Gravitational ↔ Elastic
Lifting a weight → chemical → gravitational potential
Electrical work (currents)
Chemical ↔ Electrical ↔ Radiant ↔ Thermal
Battery powering a torch → light + heat
Heating (temperature difference)
Thermal ↔ Thermal
Boiling water on a stove → thermal energy transfer
Electromagnetic waves
Radiant ↔ Thermal ↔ Chemical
Solar panels: sunlight → electrical energy
Sound waves
Acoustic ↔ Thermal
Loudspeaker: electrical → sound → some heat
Other mechanical waves (water, seismic)
Kinetic ↔ Potential ↔ Electrical (via generators)
Wave energy converter: ocean wave → electrical
Suggested diagram: Flow chart showing energy stores (kinetic, gravitational, elastic, chemical, electrical, thermal, radiant, sound) with arrows labeled by the transfer mechanisms described above.
Key Points to Remember
Energy is never created or destroyed – it only changes form (Law of Conservation of Energy).
Work done by a force transfers energy between mechanical stores.
Electrical currents transfer energy via voltage and charge movement.
Heat flows from higher to lower temperature, converting thermal energy between bodies.
Electromagnetic and sound waves carry energy through space or a medium without the need for a material carrier.
In all cases, the amount of energy transferred can be calculated using the appropriate formulae shown.