A student investigates how the resistance of a length of wire changes as the wire gets longer. Describe what resistance is and explain why a longer wire has greater resistance than a shorter wire of the same material and thickness.

Eduqas GCSE Physics — 7.1 Current, potential difference and resistance · Describe and Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Resistance is the opposition to the flow of current in a conductor.

Electrons moving through the wire collide with the ions/atoms of the material.

In a longer wire the electrons must travel a greater distance, so they experience more collisions.

More collisions give greater opposition to the flow of charge, so the resistance is higher.

Examiner tips

  • Use the exact definition of resistance – opposition to current flow. Explain the collision mechanism and link distance to number of collisions. Show the causal chain: longer wire → more collisions → higher resistance.
  • common_mistakes
  • :
  • Saying resistance is simply a property of the material, ignoring length. Forgetting to mention collisions or the distance travelled. Using vague terms like “more resistance” without explaining why.

Mark scheme (4 marks)

  1. Resistance is the opposition to the flow of current (in a component/wire)
  2. Electrons (charge carriers) collide with the ions/atoms in the wire
  3. A longer wire means more collisions occur / electrons travel a greater distance through the material
  4. More collisions means greater opposition to current flow / greater resistance

Key terms in this question

resistance

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