A balloon is rubbed against a woollen jumper. The balloon then sticks to a wall without falling. Explain why the balloon becomes charged when rubbed and why it is then attracted to the wall.

OCR GCSE Physics A: Gateway Science (J249) — P3.1 Static and charge · Explain · 4 marks · View as Markdown

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

When a balloon is rubbed against a woollen jumper, the balloon can be made to stick to a painted wall.

Model answer (4 marks)

Rubbing transfers electrons from the wool to the balloon, so the balloon gains electrons and becomes negatively charged.
The negative charge on the balloon induces a positive charge on the surface of the painted wall by redistributing the wall’s charges.
Opposite charges attract, so the negatively charged balloon is pulled towards the positively charged wall and sticks.

Examiner tips

  • Use the word ‘transfer’ to show electron movement; mention the balloon becomes negative. Explain induction: charges in the wall rearrange. Show the attraction of opposite charges.
  • common_mistakes
  • :
  • Saying the balloon becomes positive instead of negative. Forgetting to mention induction of charge on the wall. Using vague terms like ‘rub’ without explaining electron transfer.

Mark scheme (4 marks)

  1. Rubbing transfers electrons from the wool to the balloon (or from the balloon to the wool)
  2. The balloon gains electrons so becomes negatively charged
  3. The charged balloon induces a charge on the surface of the wall / redistributes charges in the wall so the near surface becomes oppositely (positively) charged
  4. Opposite charges attract, so the balloon is pulled towards the wall

Key terms in this question

attract

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