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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 the plastic comb is rubbed with a dry cloth, friction occurs between the two materials. This friction causes electrons to be transferred from the comb to the cloth, resulting in the comb losing some of its negative charge. As a consequence, the comb is left with an excess of positive charge, due to having more protons than electrons. Thus, the comb becomes positively charged.
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 by repelling positive charges within the paper, creating polarization. The side of the paper that is nearest the comb becomes negatively charged, while the opposite side remains neutral or less positively charged. This results in an attractive force between the negatively charged area of the paper and the positively charged comb, allowing the comb to pick up the small pieces of paper.
Step 3
Which of these diagrams shows the shape and direction of the electric field around a positive point charge?
Answer
The correct diagram (either A, B, C, or D) will show radial lines emanating outward from the positive charge, indicating the direction of the electric field lines which point away from the charge.
Step 4
Explain, in terms of electric fields, why a force is exerted on sphere B.
Answer
When the two metal spheres are charged, sphere A, being fixed, creates an electric field around it. Sphere B, being in that electric field, experiences a force due to the interaction of its own charge with the electric field produced by sphere A. This force is a result of the attraction or repulsion between the charges in the spheres, depending on their respective charges.