What is meant by the current–voltage characteristic of a component?

It is the graph of the current through a component against the potential difference across it, usually taken for both directions of the potential difference, which shows how the component's resistance behaves over its whole working range.

Describe the circuit used to obtain a current–voltage characteristic.

The component under test is connected in series with an ammeter and supplied from the output of a potential divider across the supply, with a voltmeter connected across the component, so that the potential difference can be varied smoothly from zero to the maximum.

How are readings for negative values of potential difference obtained?

The connections to the component are reversed, and the currents and potential differences recorded are then plotted in the third quadrant of the graph.

Describe the current–voltage characteristic of a metallic conductor kept at a constant temperature.

It is a straight line through the origin with the same gradient in both directions, showing that the current is proportional to the potential difference and the resistance is constant.

What precautions keep a metallic conductor at a constant temperature while its characteristic is taken?

Use a low current, switch the circuit on only long enough to take each pair of readings, and where necessary immerse the wire in a water bath so that any energy dissipated is carried away.

CCEA A-Level Physics 1210

Physical Quantities, Scalars and Vectors

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Resistance and Resistivity

Current–voltage characteristics of a conductor, a lamp and a diode

3 things to know
Unit AS 1

Overview

Current–voltage characteristic of a component, circuit used to obtain a current–voltage characteristic and current–voltage characteristic of a filament lamp.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why is a potential divider preferred to a rheostat in series when a characteristic is being obtained?

Key term

Explain the shape of the current–voltage characteristic of a filament lamp.

Numbers

A filament lamp carries 0.25 A at 2.0 V and 0.50 A at 6.0 V. Calculate its resistance at each point and comment.

Questions from this subtopic

Each one with the model answer underneath.

1
What is meant by the current–voltage characteristic of a component?
Model answer
It is the graph of the current through a component against the potential difference across it, usually taken for both directions of the potential difference, which shows how the component's resistance behaves over its whole working range.
2
Describe the circuit used to obtain a current–voltage characteristic.
Model answer
The component under test is connected in series with an ammeter and supplied from the output of a potential divider across the supply, with a voltmeter connected across the component, so that the potential difference can be varied smoothly from zero to the maximum.
3
Why is a potential divider preferred to a rheostat in series when a characteristic is being obtained?
Model answer
A potential divider can bring the output potential difference down to zero, whereas a series rheostat can never reduce it below the value set by its own maximum resistance, so the important low-voltage part of the characteristic would be missed.
4
How are readings for negative values of potential difference obtained?
Model answer
The connections to the component are reversed, and the currents and potential differences recorded are then plotted in the third quadrant of the graph.
5
Describe the current–voltage characteristic of a metallic conductor kept at a constant temperature.
Model answer
It is a straight line through the origin with the same gradient in both directions, showing that the current is proportional to the potential difference and the resistance is constant.
6
What precautions keep a metallic conductor at a constant temperature while its characteristic is taken?
Model answer
Use a low current, switch the circuit on only long enough to take each pair of readings, and where necessary immerse the wire in a water bath so that any energy dissipated is carried away.

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