State the apparatus needed to determine the resistivity of a metal in the form of a wire.

A length of the wire mounted alongside a metre rule, a micrometer screw gauge, a low-voltage supply, a switch, an ammeter, a voltmeter, a rheostat or protective resistor and connecting leads with a flying lead or crocodile clip to select the length under test.

Describe how the circuit is arranged so that the resistance of a chosen length of wire is measured.

The wire is connected in series with the supply and the ammeter through a flying lead that can be clipped at any point along it, and the voltmeter is connected across just the length between the fixed contact and the flying lead.

What is plotted, and what is the shape of the graph, in this determination of resistivity?

Resistance is plotted on the vertical axis against length on the horizontal axis, and the result is a straight line through the origin, since R = (ρ/A)l.

CCEA A-Level Physics 1210

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Resistance and Resistivity

Measuring the resistivity of a metal

3 things to know
Unit AS 1

Overview

Recall questions on the apparatus and method, measuring the diameter with a micrometer and why it is taken in several places, finding the area from the diameter, what is plotted and what the gradient gives, why the current is kept small, which measurement dominates the uncertainty, and the effect of contact resistance.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Outline the method used to determine the resistivity of a metal wire.

Key term

When measuring the resistivity of a metal, how should the diameter of the wire be measured, and what precautions are needed?

Key term

How is the cross-sectional area of a circular wire calculated from its diameter?

Questions from this subtopic

Each one with the model answer underneath.

1
State the apparatus needed to determine the resistivity of a metal in the form of a wire.
Model answer
A length of the wire mounted alongside a metre rule, a micrometer screw gauge, a low-voltage supply, a switch, an ammeter, a voltmeter, a rheostat or protective resistor and connecting leads with a flying lead or crocodile clip to select the length under test.
2
Outline the method used to determine the resistivity of a metal wire.
Model answer
Measure the diameter of the wire, then for each of several measured lengths pass a small current, record the current and the potential difference across that length, calculate the resistance from V/I, plot resistance against length and obtain the resistivity from the gradient and the cross-sectional area.
3
How should the diameter of the wire be measured, and what precautions are needed?
Model answer
It is measured with a micrometer screw gauge, checking first for a zero error and then taking readings at several points along the wire and at different orientations at each point, since the wire may not be perfectly uniform or perfectly circular, and averaging the results.
4
How is the cross-sectional area of a circular wire calculated from its diameter?
Model answer
The area is A = πd²/4, where d is the mean diameter in metres and A is in square metres.
5
Describe how the circuit is arranged so that the resistance of a chosen length of wire is measured.
Model answer
The wire is connected in series with the supply and the ammeter through a flying lead that can be clipped at any point along it, and the voltmeter is connected across just the length between the fixed contact and the flying lead.
6
What is plotted, and what is the shape of the graph, in this determination of resistivity?
Model answer
Resistance is plotted on the vertical axis against length on the horizontal axis, and the result is a straight line through the origin, since R = (ρ/A)l.

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Measuring the resistivity of a metal

Overview

What you need to know

Outline the method used to determine the resistivity of a metal wire.

When measuring the resistivity of a metal, how should the diameter of the wire be measured, and what precautions are needed?

How is the cross-sectional area of a circular wire calculated from its diameter?

Questions from this subtopic

State the apparatus needed to determine the resistivity of a metal in the form of a wire.

Outline the method used to determine the resistivity of a metal wire.

How should the diameter of the wire be measured, and what precautions are needed?

How is the cross-sectional area of a circular wire calculated from its diameter?

Describe how the circuit is arranged so that the resistance of a chosen length of wire is measured.

What is plotted, and what is the shape of the graph, in this determination of resistivity?

Other ways to work this

What is inside Levo

The 3-step method, run for you

Cram a whole paper in one sitting

Blank Blitz makes facts automatic

Build It gets the exam shape right

Test It catches misconceptions

Brain Breaks between sessions

Every question in Resistance and Resistivity, on a schedule.