Explain why the resistance of a filament lamp increases as the current through it increases.

AQA GCSE Physics (8463) — 4.2.1 Current, potential difference and resistance · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

As the current increases, electrons gain kinetic energy and the filament heats up.

The higher temperature causes the atoms in the filament to vibrate more strongly.

These increased vibrations lead to more frequent collisions between electrons and atoms.

The greater number of collisions makes it harder for electrons to move, so the resistance rises.

Examiner tips

  • Use the word "increase" to link current and temperature; mention electron energy. Show the chain: current → heat → vibration → collisions → resistance. Use "filament" not just "resistor" for clarity. Keep answer to 4 short sentences, one per mark.

Common mistakes

  • Confusing resistance with voltage or current. Failing to mention the filament heating. Using vague terms like "more energy" without linking to temperature.

Mark scheme (4 marks)

  1. As current increases, electrons have more energy / the filament gets hotter / temperature of the filament increases
  2. Electrons collide with atoms (in the filament / resistor)
  3. Collisions cause atoms to vibrate more
  4. Greater vibration makes it harder for electrons to flow through, so resistance increases

Key terms in this question

filament lamp · resistance · current

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