IB Physics SL B 5 9 Direct Current and Charge Flow Questions

Practise IB Physics SL B.5.9 by calculating current as charge flow and applying drift speed, carrier density and wire area.

Exam points

Define current as the rate of charge flow and use I=Δq/Δt to calculate charge, time or current in wires, liquids, batteries and electron beams.
Apply I=nqAv to determine drift speed or current from carrier density, carrier charge and cross-sectional area, including changes in wire area.
Explain how free electrons or ions act as charge carriers and how charge continuity determines current in conductors and liquids.

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Study B.5.9—Direct current and charge flow conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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In an experiment a student constructs the circuit shown in the diagram. The ammeter and the voltmeter are assumed to be ideal.

Figure for Question IB Physics SL B 5 9 Direct Current and Charge Flow Questions question 1 — IB Physics SL

A connecting wire in the circuit has a radius of 1.2 mm and the current in it is 3.5 A . The number of electrons per unit volume of the wire is $2.4 \times 10^{28} \mathrm{~m}^{-3}$ . Show that the drift speed of the electrons in the wire is $2.0 \times 10^{-4} \mathrm{~ms}^{-1}$ .

$3.5=2.4 \times 10^{28} \times \pi\left(1.2 \times 10^{-3}\right)^{2} \times 1.6 \times 10^{-19} \times v\left\|\Rightarrow v=2.0 \times 10^{-4} \mathrm{~ms}^{-1}\right\| v$

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IB Physics SL B 5 9 Direct Current and Charge Flow Questions question 1