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

Identify proper time and proper length as invariant measurements in the rest frame.
Apply time dilation and length contraction to calculate observed intervals using complete mark-scheme evidence.

[Maximum number: 1]

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