Explain why metals are good conductors of electricity, and why increasing the temperature of a metal wire causes its resistance to increase.

WJEC A-Level Physics (Wales) — 2.1 Conduction and resistance · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Metals such as copper are widely used in electrical wiring because of their low resistance. However, engineers must consider that the resistance of a metal wire changes with temperature.

Model answer (5 marks)

Metals contain free (delocalised) electrons that can move through the material
These free electrons carry charge through the metal, allowing current to flow
When temperature increases the metal ions vibrate more (with greater amplitude / more vigorously)
The more vigorously vibrating ions obstruct / collide more frequently with the free electrons
This increased obstruction makes it harder for charge to flow, so resistance increases

Examiner tips

Use the term ‘free (delocalised) electrons’ to show understanding of conduction mechanism
Explain that increased ion vibration leads to more electron‑ion collisions, which raises resistance
Keep the answer concise – 5 marks, so one sentence per point

Common mistakes

Confusing electron motion with ion motion; remember electrons move, ions vibrate
Failing to mention that resistance rises because collisions impede electron flow
Using vague terms like ‘more heat’ instead of ‘greater ion vibration’

Mark scheme (5 marks)

Metals contain free (delocalised) electrons that can move through the material
These free electrons carry charge through the metal, allowing current to flow
When temperature increases, the metal ions vibrate more (with greater amplitude / more vigorously)
The more vigorously vibrating ions obstruct / collide more frequently with the free electrons
This increased obstruction makes it harder for charge to flow, so resistance increases

Key terms in this question

resistance · conductor