Pearson International A Level Physics Core Practical 7: Determine the electrical resistivity of a material

This core practical is part of Pearson's practical-learning programme. The method below is one defensible implementation, not a confidential instruction sheet. Centres may adapt equipment while preserving the scientific purpose, controls, measurements and safety requirements.

Aim and scientific principle

Measure resistance for a conductor with known length and cross-sectional area, while limiting temperature change.

Begin by translating the title into a testable question. Identify what is deliberately changed, what is measured directly, what is calculated and what must remain controlled. Predict a relationship only after naming the mechanism. A prediction without a reason is weak; a reason without measurable variables cannot guide a practical design.

Apparatus and setup

Use test wire, micrometer, metre rule, low-voltage supply, ammeter, voltmeter, switch, variable resistor and leads. Select every measuring instrument by range and resolution, not by name alone. Draw a labelled scientific setup that shows the working geometry and exactly where readings are taken. Include a control or blank when it distinguishes the target effect from drift, contamination or background response.

Before collecting results, check zero readings, calibration, leaks, alignment or sterility as relevant. Record the instrument resolution beside the first raw-data table. If a digital device displays more digits than its underlying accuracy supports, do not treat every digit as equally certain.

Method

1. Measure diameter at several positions and directions, then calculate mean cross-sectional area.
2. Set a measured wire length and connect ammeter in series and voltmeter across only that length.
3. Use small currents, open the switch between readings and record several current-voltage pairs.
4. Find resistance from the graph gradient and calculate resistivity = RA/L.

Plan the analysis before starting. This reveals whether an additional measurement is needed for a derived quantity and prevents a completed experiment from lacking a mass, length, concentration, background or calibration value. A method should be detailed enough for another trained student to reproduce, while avoiding decorative steps that do not affect validity.

Variables and controls

• Independent variable: wire length or current for obtaining resistance.
• Dependent variable: potential difference, current and derived resistance.