AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
The strength of the magnetic field depends on the current through the wire…
Full specification wording
Electromagnetism: The strength of the magnetic field depends on the current through the wire and the distance from the wire.
Two things set the strength of the field around a straight wire: the size of the current and the distance from the wire.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 2 of 9
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Two things set the strength of the field around a straight wire: the size of the current and the distance from the wire. Increase the current and the field at any given point is stronger, which is why the field lines are drawn more densely for a larger current. Move away from the wire and the field gets weaker, which is why the concentric circles are drawn further apart further out. Nothing else on the list of tempting answers works: reversing the current only reverses the direction, and heating the wire does not strengthen the field. You can test each factor by holding a compass at a fixed distance and varying the current, then holding the current fixed and moving the compass.
What earns the marks
- Stating that increasing the current increases the strength of the magnetic field.
- Stating that the field is weaker at greater distances from the wire.
- Choosing 'increase the current in the wire' rather than changing its direction or its temperature.
- Describing a test in which only one of the two factors is changed at a time.
Common mistakes and how to put them right
Saying that reversing the direction of the current makes the field stronger.
Offering the temperature or the resistance of the wire as a factor.
Saying the field is strongest at the ends of the wire, as though it were a bar magnet.
Confusing the distance from the wire with the length of the wire.
Exam tips
- In a multiple choice item the distractors are usually direction and temperature; rule both out.
- Name the factor and the direction of the change: increase the current, so the field is stronger.
- Keep one variable fixed when you describe a test.
Try the lesson
The start of the Electromagnetism: 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
The current through a straight conducting wire is increased. What happens to the strength of the magnetic field around the wire?
Listen
Two things set the strength of the field around a straight wire: the size of the current and the distance from the wire. Increase the current and the field at any given point is stronger, which is why the field lines are drawn more densely for a larger current. Move away from the wire and the field gets weaker, which is why the concentric circles are drawn further apart further out. Nothing else on the list of tempting answers works: reversing the current only reverses the direction, and heating the wire does not strengthen the field. You can test each factor by holding a compass at a fixed distance and varying the current, then holding the current fixed and moving the compass. A strong answer earns marks for these points. stating that increasing the current increases the strength of the magnetic field. stating that the field is weaker at greater distances from the wire. choosing 'increase the current in the wire' rather than changing its direction or its temperature. describing a test in which only one of the two factors is changed at a time. Exam tip: In a multiple choice item the distractors are usually direction and temperature; rule both out.
See it
Key words
Say what each word means before you turn the card.
current and field strength
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distance from the wire
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field around a straight wire
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controlling variables
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See every definition
- current and field strength
- Increasing the current increases the strength of the magnetic field at any given point.
- distance from the wire
- The field is weaker at greater distances from the wire, which is why the concentric circles are drawn further apart further out.
- field around a straight wire
- Two things set its strength: the size of the current and the distance from the wire.
- controlling variables
- Describing a test in which only one of the two factors is changed at a time, keeping one variable fixed.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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