# Energy and the environment

> Comparing energy resources and storage by efficiency, power, emissions, reliability and life-cycle impact rather than by a single headline number.

Canonical: https://revise-gray.vercel.app/library?topic=wjec-alevel-physics.energy-environment
Last updated: 2026-08-01

Flagship subject: topics and specification statements are authored to the WJEC specification. No question in it has been through human review yet.

- Subject: [WJEC · A Level · Physics](https://revise-gray.vercel.app/library?subject=wjec-alevel-physics)
- Specification reference: Unit 4 Option D
- Difficulty: 4/5
- Assessment objectives: AO1, AO2, AO3
- Status: authored · checked · 2026-08-01

## Specification coverage

| Reference | Statement | AOs |
| --- | --- | --- |
| Unit 4 Option D(a) | compare energy resources using efficiency power reliability and capacity factor | AO2, AO3 |
| Unit 4 Option D(b) | explain the greenhouse effect and energy transfer by infrared radiation | AO1, AO2 |
| Unit 4 Option D(c) | evaluate energy-storage technologies with energy and power constraints | AO2, AO3 |
| Unit 4 Option D(d) | use life-cycle analysis and uncertainty to evaluate environmental claims | AO2, AO3 |

## Summary

Comparing energy resources and storage by efficiency, power, emissions, reliability and life-cycle impact rather than by a single headline number.

## What earns marks

- Efficiency is useful output divided by total input; a complete comparison also reports capacity factor, intermittency, power density and the time scale of demand.
- The greenhouse effect is caused by absorption and re-emission of infrared radiation; a budget must distinguish natural greenhouse warming from human-driven changes.
- Batteries, pumped storage, hydrogen and thermal storage shift energy through time but introduce losses, material constraints and infrastructure requirements.
- Life-cycle analysis includes construction, fuel extraction, operation, decommissioning and waste; uncertainty should be shown rather than hidden in a single ranking.

## Where marks are lost

- Calling an energy source 100% efficient because the fuel is free or renewable.
- Treating power and energy as interchangeable.
- Counting only operational emissions and ignoring construction or disposal stages.

## Related

- [WJEC · A Level · Physics](https://revise-gray.vercel.app/library?subject=wjec-alevel-physics)
- [Energy and the environment lesson](https://revise-gray.vercel.app/lesson?subject=wjec-alevel-physics&topic=wjec-alevel-physics.energy-environment)