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

Derive resistance ratios for changed length, radius/diameter, cross-sectional area or material using R=ρL/A.
Calculate resistivity, resistance, radius or length from data and graphs, reporting SI units and interpreting the relevant gradient or proportionality.
Relate R=ρL/A to I=nqAv, V=EL and microscopic charge transport when deriving relationships between drift speed, electric field and resistivity.
Explain or predict resistance changes caused by material choice and temperature through lattice vibration, carrier collisions and resistivity.

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Study B.5.12—Resistance and resistivity conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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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