Explain why a spark is produced when a person who has built up a static charge reaches towards a metal door handle.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A person walks across a nylon carpet wearing rubber-soled shoes. As they reach towards a metal door handle, a spark jumps between their finger and the handle.
Model answer (4 marks)
Rubbing or walking across the nylon carpet transfers electrons from the carpet to the person, leaving the person with a net static charge.
The rubber soles act as an insulator, so the charge cannot flow to the ground and it accumulates on the person.
When the person reaches for the metal door handle, a large potential difference develops between the charged person and the earthed handle.
The electric field in the air becomes strong enough that the air ionises, allowing the charge to jump from the person to the handle, producing a spark.
The rubber soles act as an insulator, so the charge cannot flow to the ground and it accumulates on the person.
When the person reaches for the metal door handle, a large potential difference develops between the charged person and the earthed handle.
The electric field in the air becomes strong enough that the air ionises, allowing the charge to jump from the person to the handle, producing a spark.
Examiner tips
- Use the word ‘transfer’ to show electron movement. Mention the rubber soles as an insulator. Explain that the handle is earthed. Show the spark as charge moving to balance the potential difference.
Common mistakes
- Confusing the carpet with the handle as the source of charge. Forgetting that the rubber soles prevent discharge to the earth. Saying the spark is caused by friction rather than a potential difference.
Mark scheme (4 marks)
- Rubbing/walking across the carpet transfers electrons between surfaces, leaving the person with a net (static) charge
- Charge builds up on the person because they are an insulator (rubber soles prevent charge flowing away to earth)
- A large potential difference / enough charge builds up between the person and the (earthed) metal handle
- The charge jumps through the air from the person to the handle (to balance the charges), producing a spark
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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