Uses of static electricity
4 marks · NormalA conveyor belt moves grains past a metal plate. The grains rub the belt and become charged.
Describe what happens if the grains are negatively charged and the metal plate is earthed.
Explain how static electricity can be used to separate the grains from unwanted materials (chaff) using a charged conveyor and earthed plate.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) The negatively charged grains experience an attractive force towards the earthed metal plate, which is neutral and can induce a positive charge by attracting positive charges to the surface closest to the grain.
(b) Because the grains are charged and the chaff is not, the grains are attracted to the plate while the chaff falls away, so static electricity is used to separate the two.
Common mistakes: Not mentioning earthed plate effect
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Describes attractive force between negatively charged grains and earthed (neutral) plate.
B2 (a) · 1 mark · Mentions induction of positive charge or redistribution on plate surface.
B3 (b) · 1 mark · Explains that charged grains are pulled towards plate, chaff is unaffected.
B4 (b) · 1 mark · Uses static electricity to separate desired grains from waste.
Worked solution
a) The negatively charged grains are attracted towards the earthed metal plate, which induces a positive charge on the plate's surface closest to the grains, causing attraction.
b) As the grains are charged and chaff is not, only the grains are attracted to the plate. This way, static electricity can be used to collect the grains or divert them, separating them from the chaff.