A factory uses a plastic film to wrap boxes of electronic components. Fig. 1 shows the film passing quickly over a rubber roller. After the film is cut, wor...
Question 1 Report
A factory uses a plastic film to wrap boxes of electronic components. Fig. 1 shows the film passing quickly over a rubber roller. After the film is cut, workers find that it clings to the metal frame and attracts dust particles. The factory engineer proposes fitting a metal strip connected to Earth beside the roller.
(a) State how the plastic film becomes charged as it passes over the roller. [1]
(b) Explain why charged film can attract an uncharged dust particle. [2]
(c) Describe how the earthed metal strip can reduce the charge on the film. [2]
Answer Details
(a) The plastic film becomes charged by friction as it rubs against the rubber roller. This involves transfer of electrons. [1]
(b) A charged film causes charge separation, or induction, in an uncharged dust particle. The side nearer the film gains an opposite charge and is attracted more strongly than any repulsion from the farther side, giving a net attraction. [2]
(c) The earthed metal strip conducts charge. Charge flows between the film and Earth, reducing or neutralising the film's net charge. [2]
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