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A student rubs a plastic comb with a dry cloth to give the comb a positive electric charge - Edexcel - GCSE Physics - Question 4 - 2018 - Paper 1
Question 4
A student rubs a plastic comb with a dry cloth to give the comb a positive electric charge. Figure 6 shows the charged plastic comb picking up small pieces of paper.... show full transcript
Worked Solution & Example Answer:A student rubs a plastic comb with a dry cloth to give the comb a positive electric charge - Edexcel - GCSE Physics - Question 4 - 2018 - Paper 1
Step 1
Explain how rubbing the comb with a dry cloth gives the comb a positive electric charge.
Answer
When a plastic comb is rubbed with a dry cloth, friction between the two materials causes electrons to transfer from the comb to the cloth. As electrons are negatively charged particles, the removal of these electrons results in the comb having an excess of positive charge. This occurs because the comb loses more negatively charged electrons than it gains from the cloth, leaving it with a net positive charge.
Step 2
Explain how the positively-charged plastic comb picks up the small pieces of paper.
Answer
The positively charged comb induces a negative charge on the part of the paper closest to it. This happens because the electric field of the comb repels positive charges in the paper and attracts negative charges, causing a separation of charges within the paper. The attractive force between the positively charged comb and the induced negative charge on the paper pieces is strong enough to overcome the weight of the paper, allowing the comb to pick them up.
Step 3
Which of these diagrams shows the shape and direction of the electric field around a positive point charge?
Answer
The correct diagram is the one that illustrates radial lines emanating outward from a central point, indicating the direction of the electric field away from a positive point charge.
Step 4
Explain, in terms of electric fields, why a force is exerted on sphere B.
Answer
When both spheres are given a negative charge, their electric fields interact. Sphere A, being fixed, creates an electric field that extends into the space around it. Sphere B, being insulated and movable, is influenced by this electric field. Despite both spheres possessing negative charge, the force exerted on sphere B is a result of the interaction with the electric field generated by sphere A, which ultimately leads to repulsive forces acting on sphere B as it approaches.