AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
When a current flows through a conducting wire a magnetic field is…
Full specification wording
Electromagnetism: When a current flows through a conducting wire a magnetic field is produced around the wire. The strength of the magnetic field depends on the current through the wire and the distance from the wire.
A current-carrying conductor is surrounded by a magnetic field.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 1 of 6
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A current-carrying conductor is surrounded by a magnetic field. You can detect it by placing a plotting compass near a straight wire: when the current is switched on, the compass needle deflects, showing a field is present. The field forms concentric circles around the wire, with the direction given by the right-hand grip rule: point your right thumb along the conventional current, and your curled fingers show the field direction. Field strength increases when the current increases, and decreases as you move further from the wire. Reversing the current reverses the field direction. This principle underpins electromagnets, motors and transformers, so understanding how current and distance affect the field is essential.
What earns the marks
- A magnetic field is produced around a conducting wire only when a current flows through it.
- The field lines around a straight wire are concentric circles centred on the wire.
- Increasing the current through the wire increases the strength of the magnetic field.
- Increasing the distance from the wire decreases the strength of the magnetic field.
- The direction of the magnetic field reverses if the direction of the current reverses.
- The right-hand grip rule predicts the field direction: thumb along conventional current, fingers curl in field direction.
Common mistakes and how to put them right
Thinking a magnetic field exists around a wire even with no current.
Put it right by stating that the field is produced by the current, so no current means no magnetic field.
Believing field strength is the same everywhere around the wire.
Put it right by explaining that field strength decreases with distance from the wire.
Confusing the direction of conventional current with electron flow.
Put it right by using conventional current from positive to negative in the right-hand grip rule.
Exam tips
- When describing the field pattern, state that the lines are concentric circles around the wire and that the spacing indicates field strength.
- Use the right-hand grip rule explicitly in answers about direction, naming the thumb as current and fingers as field.
- For questions comparing field strength, link your answer to both current and distance rather than only one factor.
Try the lesson
The start of the Electromagnetism: When a current flows through a conducting wire a magnetic field is produced around the wire. The strength of the magnetic field depends on the current through the wire and the distance from the wire. lesson, made from checked teaching notes for this specification point.
Have a go first
What is produced around a conducting wire when a current flows through it?
Listen
A current-carrying conductor is surrounded by a magnetic field. You can detect it by placing a plotting compass near a straight wire: when the current is switched on, the compass needle deflects, showing a field is present. The field forms concentric circles around the wire, with the direction given by the right-hand grip rule: point your right thumb along the conventional current, and your curled fingers show the field direction. Field strength increases when the current increases, and decreases as you move further from the wire. Reversing the current reverses the field direction. This principle underpins electromagnets, motors and transformers, so understanding how current and distance affect the field is essential. A strong answer earns marks for these points. A magnetic field is produced around a conducting wire only when a current flows through it. The field lines around a straight wire are concentric circles centred on the wire. Increasing the current through the wire increases the strength of the magnetic field. Increasing the distance from the wire decreases the strength of the magnetic field. A common slip: Thinking a magnetic field exists around a wire even with no current. Instead, stating that the field is produced by the current, so no current means no magnetic field. Exam tip: When describing the field pattern, state that the lines are concentric circles around the wire and that the spacing indicates field strength.
Key words
Say what each word means before you turn the card.
Magnetic effect of a current
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Field strength and distance
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Direction of magnetic fields
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See every definition
- Magnetic effect of a current
- A magnetic field is produced around a conducting wire when a current flows through it.
- Field strength and distance
- The strength of the magnetic field depends on the current through the wire and the distance from the wire.
- Direction of magnetic fields
- The direction of the magnetic field reverses if the direction of the current reverses.
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