# Electric circuits

> Current, potential difference and resistance, Kirchhoff's laws, resistivity, EMF and internal resistance, potential dividers, and the I–V characteristics of components.

Canonical: https://revise-gray.vercel.app/library?topic=wjec-alevel-physics.electric-circuits
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 2.4
- Difficulty: 3/5
- Assessment objectives: AO1, AO2
- Status: authored · checked · 2026-08-01

## Specification coverage

| Reference | Statement | AOs |
| --- | --- | --- |
| Unit 2.4(a) | recall the key definitions and relations for electric circuits | AO1 |
| Unit 2.4(b) | apply the relations for electric circuits to solve numerical problems | AO2 |
| Unit 2.4(c) | interpret or evaluate results related to electric circuits | AO2, AO3 |
| Unit 2.4(e) | analyse power dissipation in resistors and efficiency of electrical devices | AO2 |
| Unit 2.4(f) | interpret I-V characteristics for ohmic conductors filament lamps and diodes | AO2, AO3 |
| Unit 2.4(g) | describe the potentiometer and its use for comparing emfs | AO1, AO2 |
| Unit 2.4(h) | evaluate experimental errors in electrical measurements | AO3 |

## Summary

Current, potential difference and resistance, Kirchhoff's laws, resistivity, EMF and internal resistance, potential dividers, and the I–V characteristics of components.

## What earns marks

- Kirchhoff: charge is conserved at a junction, energy is conserved around a loop.
- ε = I(R + r): the terminal p.d. falls as current rises because of lost volts Ir.
- Resistivity ρ = RA/L — a material property, unlike resistance.
- A filament lamp's resistance rises with temperature, giving a curved I–V characteristic.

## Where marks are lost

- Treating EMF and terminal p.d. as identical.
- Using length in cm in a resistivity calculation.
- Adding parallel resistances directly.

## Related

- [WJEC · A Level · Physics](https://revise-gray.vercel.app/library?subject=wjec-alevel-physics)
- [Electric circuits lesson](https://revise-gray.vercel.app/lesson?subject=wjec-alevel-physics&topic=wjec-alevel-physics.electric-circuits)