Why wire diameter matters in resistivity
Resistivity is calculated from several measurements. Diameter contributes twice its percentage uncertainty through the cross-sectional area.
Follow the reasoning
- Measure diameter at several positions and directions.
- Estimate the uncertainties in voltage, current, length and diameter.
- Combine their percentage contributions with the correct powers.
Try it in a past paper 6
Open the question, then use its mark scheme to check your work.
Question 15
Combine mass and length uncertainties when calculating density.
Build the supporting skills. Practise Measurements and uncertainty before exploring this connection. This question has not been checked as a combined example of the connection.
Question 22
Evaluate a refractive-index identification and describe an accurate critical-angle measurement.
Build the supporting skills. Practise Measurements and uncertainty before exploring this connection. This question has not been checked as a combined example of the connection.
Question 2
Use repeated diameter readings, density and upthrust to analyse a floating cylinder.
Build the supporting skills. Practise Measurements and uncertainty before exploring this connection. This question has not been checked as a combined example of the connection.
Question 3
Compare wire resistance and charge-carrier number density.
Build the supporting skills. Practise Resistivity before exploring this connection. This question has not been checked as a combined example of the connection.
Show 2 more paper references
Question 4
Interpret the gradient of a resistance–length graph.
Build the supporting skills. Practise Resistivity before exploring this connection. This question has not been checked as a combined example of the connection.
Question 9
Compare current, carrier density and drift speed in two wires.
Build the supporting skills. Practise Resistivity before exploring this connection. This question has not been checked as a combined example of the connection.
A curated collection checked against the question papers and mark schemes; not a complete past-paper catalogue. Links open official OCR PDFs in a new tab.
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Specification outcomes (4)
- 4.2.4(a)(i) Define resistivity using R = ρL / A.
- 4.2.4(a)(ii) Use techniques and procedures to determine the resistivity of a metal.
- 2.2.1(a) Understand systematic errors (including zero errors) and random errors in measurements.
- 2.2.1(c) Calculate absolute and percentage uncertainties when data are combined by addition, subtraction, multiplication, division or raising to powers.