A student rubs a balloon on their hair. The balloon becomes negatively charged. Explain why two balloons, both charged in this way, repel each other when brought close together.

Eduqas GCSE Physics — 7.3 Static electricity – forces and electric fields · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Rubbing transfers electrons from the hair to the balloon, giving each balloon a surplus of electrons.
Both balloons therefore carry the same type of charge – negative.
Like charges repel, so the balloons push away from one another.
The repulsive force is exerted through the electric field, so the balloons do not need to touch to repel.

Examiner tips

  • Use the word "transfer" to show electron movement. Mention that both balloons are negatively charged. State that like charges repel. Explain that the force acts via the electric field, not contact.

Common mistakes

  • Saying the balloons are positively charged. Forgetting to mention the electric field. Using vague terms like "push apart" without linking to charge type.

Mark scheme (4 marks)

  1. Rubbing transfers electrons from the hair to the balloon
  2. Both balloons carry the same type of charge (negative)
  3. Like charges repel
  4. The repulsive force acts without the balloons touching, through the electric field

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