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AQA GCSE · Question 04.1 · Electricity
A student with long hair touches the negatively charged metal dome of a static electricity generator (a Van de Graaff generator). Her hair stands on end.
Explain why the student's hair stands up on end.
A student with long hair touches the negatively charged metal dome of a static electricity generator (a Van de Graaff generator). Her hair stands on end.
Explain why the student's hair stands up on end.
How to approach this question
1. Start by explaining how the hair becomes charged. What type of charge moves from the dome to the student?
2. What is the charge on each strand of hair now?
3. What is the rule for forces between like charges? Apply this rule to the individual strands of hair.
Full Answer
1. As the student is touching the dome, negative charge (electrons) is transferred from the dome to the student, including her hair.
2. This causes each individual strand of hair to become negatively charged.
3. Since like charges repel, the negatively charged strands of hair repel each other, causing them to spread out and stand on end.
The dome of the Van de Graaff generator is negatively charged, meaning it has an excess of electrons. When the student touches the dome, these excess electrons are conducted through her body, including to each strand of her hair. As a result, every strand of hair gains an excess of electrons and becomes negatively charged. Objects with the same type of charge exert a repulsive force on each other. Therefore, each negatively charged strand of hair repels its neighbouring strands, causing them to push away from each other and from her head, making them stand on end.
Common mistakes
✗ Just saying "static electricity builds up" without explaining the charge transfer.
✗ Forgetting to mention that like charges repel.
✗ Confusing negative and positive charge transfer.
Practice the full AQA GCSE Physics Higher Tier Paper 1
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