(a) The current I in a metal wire is given by the expression
I = Anve.
State what is meant by the symbols A and n.
(b) The diameter of a wire XY varies linearly with distance along the wire as shown in Fig. 7.1.
[Figure 7.1]
There is a current I in the wire. At end X of the wire, the diameter is d and the average drift speed of the free electrons is v_x. At end Y of the wire, the diameter is d/2.
On Fig. 7.2, sketch a graph to show the variation of the average drift speed with position along the wire between X and Y.
[Figure 7.2]

Q: What topic does this question test?

This question tests Electricity in A-Level Physics (syllabus code 9702). It is worth 4 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Physics Oct/Nov 2018 examination, Paper 2 Variant 2 (9702_w18_qp_22.pdf).

Question

(a) The current I in a metal wire is given by the expression
I = Anve.
State what is meant by the symbols A and n.
(b) The diameter of a wire XY varies linearly with distance along the wire as shown in Fig. 7.1.
[Figure 7.1]
There is a current I in the wire. At end X of the wire, the diameter is d and the average drift speed of the free electrons is v_x. At end Y of the wire, the diameter is d/2.
On Fig. 7.2, sketch a graph to show the variation of the average drift speed with position along the wire between X and Y.
[Figure 7.2]

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