O-LevelPhysicsElectricity5054/21 · Oct/Nov 2021 · Q56 Marks

A plastic rod that is initially neutral is rubbed with a woollen cloth. After the rod has been rubbed, it is positively charged.

(a)(i)Explain, in terms of particles, why the rod is now positively charged.[1]
(a)(ii)State what happens to the woollen cloth.[1]
(b)(i)An uncharged, conducting sphere is suspended from an insulating thread. The positively charged rod is placed near to the sphere, as shown in Fig. 5.1. [Figure 5.1] On Fig. 5.1, draw the distribution of charge on the sphere.[2]
(b)(ii)Explain why the sphere is pulled towards the rod.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

[B1] electrons are transferred from rod (on to cloth)
[B1] it/ the cloth becomes negatively charged
[M1] more negative (than positive) signs on left of sphere and more positive (than negative) signs on right
[A1] equal numbers of positive and negative signs and six or fewer
[B1] negative charges/electrons (on sphere) attracted by positive charges (on rod)
[B1] force of attraction greater than repulsion (of positive charges) or distance between negative (on sphere) and positive charges (on rod) less than distance between positive and positive

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