Energy Resources and Efficiency
PhysicsΒ· 1.7.3Β· 25 min read
1. Core: Classification of Energy Resourcesβ β ββββ± 8 min
Renewable vs Non-Renewable Resources
Non-renewable resources (fossil fuels, nuclear fuel) are finite and used faster than they form. Renewable resources (solar, wind, hydro, geothermal, tidal, biofuels) are replenished continually over human timescales.
Each resource has distinct tradeoffs for large-scale electricity generation, based on cost, reliability, environmental impact, and geographic availability:
Fossil fuels (coal, oil, gas): High energy density, reliable output, but release greenhouse gases/air pollution; finite supplies.
Nuclear: No operating carbon emissions, high consistent output, but produces long-lived radioactive waste and high decommissioning costs.
Solar: No running costs, zero operating emissions, but output depends on daylight/weather, high upfront installation cost.
Wind: Low running costs, zero operating emissions, but output varies with wind speed, may cause noise/visual pollution.
Hydroelectric: Reliable, meets peak demand, but requires flooding large land areas and displaces local communities.
Geothermal: Consistent output, low emissions, only viable in areas with high tectonic activity.
Tidal: Predictable output, zero emissions, limited to coastal locations with large tidal ranges.
Biofuels: Carbon-neutral if crops are replanted, but requires large farmland areas that could be used for food production.
State one advantage and one disadvantage of using tidal energy to generate electricity, compared to coal-fired power stations.
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Step 1: Identify advantage of tidal over coal: Tidal energy produces no carbon dioxide emissions during operation, while coal releases large volumes of greenhouse gases that drive climate change.
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Step 2: Identify disadvantage of tidal: Tidal power stations can only be built in suitable coastal locations with large tidal ranges, while coal power stations can be built in almost any location near fuel transport links.
Exam tip:
Always link your advantage/disadvantage to the specific use case asked, e.g. solar is ideal for remote off-grid homes even if output is variable.
2. Core: Understanding Energy Efficiency (Qualitative)β β ββββ± 6 min
Efficiency
A measure of how much of the total energy input to a device is transferred into useful energy output. A more efficient device wastes less of the input energy.
Example:
An LED lamp is more efficient than a filament lamp because a greater fraction of the electrical energy supplied is transferred to useful light, rather than being wasted as heat.
In every energy transfer, the total energy input is shared between useful energy output and wasted energy. By the law of conservation of energy: total energy input = useful energy output + wasted energy. Wasted energy is almost always dissipated to the surroundings as thermal energy (heat).
A filament lamp and an LED lamp both give out the same amount of light. Explain, in terms of useful and wasted energy, why the LED lamp is described as more efficient.
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Step 1: For the same useful light output, the LED lamp takes in less total electrical energy than the filament lamp.
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Step 2: The filament lamp wastes a large fraction of its input energy as heat, while the LED lamp wastes much less.
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Step 3: Because a greater fraction of the LED lamp's input energy becomes useful light, it is more efficient (no calculation is required at Core level).
3. Extended: Efficiency Calculations and Sankey Diagramsβ β β β βExtended onlyβ± 9 min
Efficiency (quantitative)
The fraction of the total energy input to a system that is converted to useful energy output. It has no units, and can be expressed as a decimal between 0 and 1, or a percentage between 0% and 100%.
Example:
A light bulb that converts 10 J of electrical energy to 1 J of light energy has an efficiency of 0.1 or 10%.
An electric motor uses 2000 J of electrical energy to lift a box, transferring 600 J to gravitational potential energy in the box. Calculate the efficiency of the motor as a percentage.
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Step 1: Identify values: Total input energy = 2000 J, useful output energy = 600 J.
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Final answer: 30%
Sankey Diagram
Scaled diagram that shows energy flow through a system, with the width of each arrow proportional to the amount of energy it represents. The leftmost arrow is total input energy, right arrows split into useful output and wasted energy streams.
You may also calculate efficiency using power values (since power is energy per unit time), using the same ratio formula:
A Sankey diagram for an electric heater shows 1000 J of electrical input energy, 950 J of useful heat output, and 50 J of wasted sound energy. Calculate the efficiency of the heater, and explain why it is much higher than most other household appliances.
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Step 1: Substitute values into the efficiency formula:
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Step 2: Explanation: The purpose of a heater is to produce heat, so almost all wasted energy from electrical resistance is also released as heat, meaning very little energy is lost to other forms like sound or light.
Exam tip:
When reading Sankey diagrams, always add up all output arrows to confirm they match the input arrow, to avoid missing wasted energy streams.
4. Common Pitfalls
Wrong move:
Classifying nuclear fuel as a renewable resource
Why:
Nuclear fuel uses finite uranium reserves that are not replenished over human timescales
Correct move:
Classify nuclear fuel as a non-renewable resource
Wrong move:
Calculating efficiency as total input divided by useful output
Why:
This produces values greater than 1, which violates the law of conservation of energy
Correct move:
Always divide useful output by total input, and confirm your result is β€ 100%
Wrong move:
Claiming biofuels produce zero carbon emissions
Why:
Burning biofuels releases carbon dioxide; emissions are only offset if the source crops are replanted to absorb COβ
Correct move:
State that sustainably produced biofuels are carbon-neutral, not zero-emission
Wrong move:
Mixing energy and power values in efficiency calculations for Extended questions
Why:
Inconsistent units produce invalid, non-unitless efficiency values
Correct move:
Convert units first (e.g. multiply power by time to get energy) before applying the efficiency formula
Wrong move:
Stating renewable resources are always cheaper than non-renewable resources
Why:
Many renewables have very high upfront installation costs, even if running costs are low
Correct move:
Distinguish between upfront capital costs and ongoing running costs when comparing resource costs
5. Quick Reference Cheatsheet
Concept | Core Key Fact/Formula | Extended Add-on |
|---|---|---|
Resource Classification | Non-renewable: fossil fuels, nuclear; Renewable: solar, wind, hydro, tidal, geothermal, biofuels | Interpret Sankey diagrams (arrow width = energy quantity) |
Efficiency | Qualitative: the fraction of input energy transferred usefully; the rest is wasted (mostly as heat) | ; also = useful power Γ· total power |
Key Rule | Efficiency can never exceed 100% (conservation of energy) | Sum of output energy flows = total input energy flow |
6. Frequently Asked
How do I calculate efficiency as a percentage?
Multiply the ratio of useful output energy to total input energy by 100:
Are all renewable resources carbon-neutral?
Most renewable resources produce far lower emissions than fossil fuels, but some (e.g. biofuels) release carbon during harvesting/processing, so they are not always 100% carbon-neutral.
Going deeper
What's Next
Now that you have mastered energy resources and efficiency for CIE IGCSE Physics 0625 Unit 1, you can move on to studying work and power, the next core subtopic in the Motion, Forces and Energy unit. You should also practice structured exam questions on this topic to familiarize yourself with common phrasing, especially for Extended questions that require comparing multiple energy resources for specific use cases. Make sure you can apply efficiency calculations to a range of systems, from light bulbs to grid-scale power stations, as these appear frequently in Extended papers.