A student runs a plastic comb through their dry hair several times. The comb then attracts small pieces of tissue paper without touching them. Explain why the comb becomes charged when passed through the hair, and why the uncharged pieces of tissue paper are then attracted to the comb.

Pearson Edexcel International GCSE Physics (4PH1) — 2.3 Electric charge · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Friction between the comb and the hair causes electrons to be transferred from the hair to the comb. The comb therefore gains electrons and becomes negatively charged. The negative charge on the comb repels electrons in the nearby tissue paper, leaving the surface of the paper nearest the comb positively charged. The negatively charged comb then attracts this positively charged surface, so the tissue paper is drawn to the comb.

Examiner tips

  • Use the word ‘friction’ and ‘electrons’ to show understanding of charge transfer.
  • Explain that the comb becomes negative and the paper becomes positive by induction.
  • Show the attraction between opposite charges.
  • Keep the answer concise – 4 marks can be earned with 4 clear points.

Common mistakes

  • Saying the comb becomes positive instead of negative.
  • Failing to mention that the paper is neutral before attraction.
  • Using vague terms like ‘static’ without explaining charge transfer.

Mark scheme (4 marks)

  1. Friction between the comb and hair causes electrons to transfer from the hair to the comb (or equivalent: the comb gains electrons from the hair).
  2. The comb gains electrons and therefore becomes negatively charged.
  3. The negative charge on the comb repels electrons (negative charges) in the nearby tissue paper, so the surface of the tissue paper closest to the comb acquires a positive charge.
  4. The negatively charged comb attracts the positively charged surface of the tissue paper because unlike/opposite charges attract.

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