Charging materials by friction
2 marks · NormalA plastic ruler is charged by rubbing it with a duster. The ruler can then pick up small pieces of paper.
Explain why the charged ruler attracts the paper pieces, even if they are uncharged.
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The charged ruler induces a charge in the paper, attracting the opposite charge and pulling the paper towards it.
(a) The charged ruler induces an opposite charge on the side of the paper closest to it, creating a force of attraction between them.
Also accept: Charged ruler polarises the paper; opposite charges attract.
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Marking points
M1 (a) · 1 mark · Mentions induction or polarisation of charge in the paper.
A1 (a) · 1 mark · States that opposite charges attract, causing the paper to be pulled towards the ruler.
Worked solution
The electrostatically charged ruler induces a charge of the opposite sign on the nearer side of the paper pieces. The result is an attractive force between the oppositely charged areas, pulling the paper towards the ruler.