Understanding Energy resources and energy transfers: Edexcel IGCSE Physics Explained

Energy is the thread that connects every section of the physics specification. Understanding how energy is stored, transferred and calculated is essential for both papers and for making sense of the physical world.

The energy resources and energy transfers edexcel igcse section covers four topics: units, energy transfers, work and power, and energy resources and electricity generation. This section is commonly examined, and the calculations it introduces (efficiency, work done, kinetic energy, gravitational potential energy and power) appear across both papers of the edexcel igcse physics energy resources and energy transfers specification.

These edexcel igcse physics revision notes walk you through every concept and equation you need. Think of energy like the currency of physics: every process involves spending it, saving it, or converting it from one form to another. Once that idea clicks, the rest follows naturally.

Units for energy

Energy transfers

Energy stores

The specification identifies eight energy stores. You need to name them and describe how energy moves between them:

• Chemical: energy stored in fuels, food and batteries
• Kinetic: energy stored in moving objects
• Gravitational potential: energy stored in objects raised above the ground
• Elastic potential: energy stored in stretched or compressed materials
• Thermal: energy stored in hot objects (related to the temperature and mass of the material)
• Magnetic: energy stored in magnetic fields
• Electrostatic: energy stored in electric fields
• Nuclear: energy stored in atomic nuclei

Energy is transferred between stores by four pathways: mechanically (by forces), electrically (by current), by heating, and by radiation (light and sound).

Conservation of energy

Energy cannot be created or destroyed, only transferred from one store to another. The total energy in a closed system remains constant. This is the principle of conservation of energy, and it underpins every energy calculation in the igcse 4ph1 energy resources and energy transfers specification.

Efficiency

No device transfers all its input energy usefully. Some energy is always dissipated, typically as thermal energy. Efficiency measures how much of the input energy becomes useful output:

efficiency = (useful energy output / total energy input) x 100%

Sankey diagrams

A Sankey diagram is a visual way of showing energy transfers. The input arrow on the left splits into useful output (continuing straight) and wasted energy (branching off, usually downward). The width of each arrow is proportional to the energy it represents. If the input is 100 J and the useful output is 40 J, the useful arrow is 40% as wide as the input, and the wasted arrow is 60% as wide.

Thermal energy transfer

Thermal energy is transferred by three mechanisms:

• Conduction: Vibrating particles pass kinetic energy to neighbouring particles. Best in solids (especially metals), poor in gases. Metals conduct well because free electrons transfer energy rapidly.
• Convection: Heated fluid (liquid or gas) expands, becomes less dense, and rises. Cooler, denser fluid sinks to replace it, setting up a convection current. Convection does not occur in solids.
• Radiation: Energy transferred by infrared electromagnetic waves. Does not require a medium. Dark, matt surfaces are good emitters and absorbers; light, shiny surfaces are poor emitters and good reflectors.

Reducing unwanted energy transfer is practical physics: cavity wall insulation traps air (poor conductor) to reduce conduction, loft insulation reduces convection and conduction, double glazing traps air between panes, and reflective foil behind radiators reduces radiation loss.

Work and power

Work done

Work is done when a force moves an object in the direction of the force. Work done = force x distance moved in the direction of the force, W = F x d. The unit of work is the joule (J). Work done equals energy transferred: if you do 200 J of work lifting a box, 200 J of energy has been transferred to the gravitational potential store.

Gravitational potential energy

GPE = m x g x h, where m is mass (kg), g is gravitational field strength (N/kg), and h is height (m).

Kinetic energy

KE = 0.5 x m x v², where m is mass (kg) and v is speed (m/s).

Conservation link

When an object falls freely (ignoring air resistance), gravitational potential energy converts to kinetic energy. At the top, GPE is maximum and KE is zero. At the bottom, KE is maximum and GPE is zero. The total (GPE + KE) stays constant. If air resistance acts, some energy is transferred to the thermal store of the surrounding air.

Power

Power is the rate of energy transfer or the rate of doing work: P = W / t, where P is power in watts (W), W is work done (or energy transferred) in joules (J), and t is time in seconds (s). One watt equals one joule per second.

Energy resources and electricity generation

Electricity is generated by spinning a turbine connected to a generator. The energy source determines how the turbine is driven:

The exam often asks you to compare renewable and non-renewable sources, or to evaluate a particular source for a given situation. The key is to match advantages and disadvantages to the context of the question.

Common mistakes in energy

1. Saying energy is "used up." Energy is never used up; it is transferred from one store to another. The correct language is that energy is dissipated (spread out into the surroundings as thermal energy) so that it is no longer useful.
2. Forgetting to square the velocity in KE. KE = 0.5 x m x v². If v = 10 m/s, v² = 100, not 10. This is one of the most frequent arithmetic errors in the edexcel exam.
3. Getting efficiency above 100%. If your calculation gives an efficiency over 100%, you have divided the wrong way round. Useful output is always less than total input.
4. Confusing power and energy. Power is the rate of energy transfer (joules per second). Energy is the total amount transferred. A 100 W bulb running for 10 s transfers 1000 J, not 100 J.
5. Mixing up conduction, convection and radiation. Conduction requires contact between particles. Convection requires fluid movement. Radiation requires no medium at all.

Self-check: edexcel igcse physics practice questions

1. A lamp has an input power of 60 W and produces 15 W of useful light. Calculate its efficiency.
2. A 3 kg object is dropped from a height of 10 m. Taking g = 10 N/kg, calculate the speed just before it hits the ground (ignore air resistance).
3. A force of 200 N moves a box 8 m in 4 s. Calculate the work done and the power.
4. Name two advantages and two disadvantages of generating electricity from wind.
5. Draw a Sankey diagram for a device that receives 400 J of input energy, produces 300 J of useful output and wastes 100 J as thermal energy.

Answers: (1) (15 / 60) x 100% = 25%; (2) GPE at top = KE at bottom, m x g x h = 0.5 x m x v², 10 x 10 = 0.5 x v², v² = 200, v = 14.1 m/s; (3) W = 200 x 8 = 1600 J, P = 1600 / 4 = 400 W; (4) Advantages: no fuel cost, no carbon emissions. Disadvantages: intermittent (depends on wind), visual impact on landscape; (5) Input arrow 400 J wide, splits into 300 J useful (straight) and 100 J wasted (branching down).

These edexcel igcse physics notes give you the complete energy section of the specification in one place. The edexcel igcse physics explained approach used here makes each concept concrete with real numbers and real worked examples. Work through them actively, and this part of the exam will feel like familiar territory.