IB Physics HL B 5 12 Resistance and Resistivity Questions

Practise IB Physics HL B.5.12 by scaling resistance with wire geometry, deriving resistivity from data, and linking macroscopic results to charge transport.

Exam points

Explain the relativity of simultaneity for events separated in space.
Use Lorentz transformations to determine whether events are simultaneous in different inertial frames using complete evidence.

[Maximum number: 2]

A cable consisting of many copper wires is used to transfer electrical energy from an alternating current (ac) generator to an electrical load. The copper wires are protected by an insulator.

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The cable consists of 32 copper wires each of length 35 km . Each wire has a resistance of $64 \Omega$ . The cable is connected to the ac generator which has an output power of 110 MW when the peak potential difference is 150 kV . The resistivity of copper is $1.7 \times 10^{-8} \Omega \mathrm{~m}$ .
output power =110 MW

Calculate the radius of each wire.

$\begin{aligned} \text{area} &= \frac{1.7\times10^{-8}\times35\times10^{3}}{64}=9.3\times10^{-6}\ \mathrm{m^2}\\ \text{radius} &= \sqrt{\frac{9.3\times10^{-6}}{\pi}}=0.00172\ \mathrm{m} \end{aligned}$

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IB Physics HL B 5 12 Resistance and Resistivity Questions question 1