AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Students should be able to recall the factors that affect the direction of…
Full specification wording
Induced potential (HT only): Students should be able to recall the factors that affect the direction of the induced potential difference/induced current.
Only two things set which way the induced potential difference points, and both of them are reversals.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 6 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Only two things set which way the induced potential difference points, and both of them are reversals. Push a magnet into a coil and the galvanometer needle swings one way; pull it out and it swings the other, because the movement has reversed. Turn the magnet round so that the south pole goes in first and the needle swings the other way again, because the field direction has reversed. Make both changes at once and the two reversals cancel, so the deflection is back where it started. That is why a coil spinning steadily in a fixed field gives a potential difference that reverses twice per turn: each side swaps from moving up through the field to moving down through it.
What earns the marks
- Reversing the direction of the relative motion reversing the induced potential difference.
- Reversing the direction of the magnetic field, by turning the magnet round, reversing it as well.
- Stating that making both reversals together leaves the direction unchanged.
- The induced potential difference reversing twice per revolution, because each side of a rotating coil changes from moving up through the field to moving down through it.
Common mistakes and how to put them right
Believing that a faster movement can change the direction, when speed only changes the size.
Assuming that holding the magnet still inside the coil keeps the needle deflected to one side.
Using the left hand rule, which predicts a force and not an induced current.
Saying the needle deflects the same way on the way in and on the way out.
Exam tips
- Sketch the two reversals separately and then combine them, so you do not lose track of a double reversal.
- Describe what the galvanometer needle does, left or right, rather than calling the reading positive or negative.
- In a spinning coil question, tie each reversal to the moment a side crosses the top or the bottom of its circle.
Try the lesson
The start of the Induced potential (HT only): Students should be able to recall the factors that affect the direction of the induced potential difference/induced current. lesson, made from checked teaching notes for this specification point.
Have a go first
A straight wire is pushed downwards through a horizontal magnetic field. Reversing which single factor reverses the direction of the induced current in the wire?
Listen
Only two things set which way the induced potential difference points, and both of them are reversals. Push a magnet into a coil and the galvanometer needle swings one way; pull it out and it swings the other, because the movement has reversed. Turn the magnet round so that the south pole goes in first and the needle swings the other way again, because the field direction has reversed. Make both changes at once and the two reversals cancel, so the deflection is back where it started. That is why a coil spinning steadily in a fixed field gives a potential difference that reverses twice per turn: each side swaps from moving up through the field to moving down through it. A strong answer earns marks for these points. reversing the direction of the relative motion reversing the induced potential difference. reversing the direction of the magnetic field, by turning the magnet round, reversing it as well. stating that making both reversals together leaves the direction unchanged. the induced potential difference reversing twice per revolution, because each side of a rotating coil changes from moving up through the field to moving down through it. Exam tip: Sketch the two reversals separately and then combine them, so you do not lose track of a double reversal.
Key words
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direction of the induced potential difference
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reversing the motion
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reversing the poles
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two reversals per revolution of a coil
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See every definition
- direction of the induced potential difference
- Set by only two things, the direction of the relative motion and the direction of the magnetic field, and both of them are reversals.
- reversing the motion
- Pulling a magnet out of a coil instead of pushing it in makes the galvanometer needle swing the other way.
- reversing the poles
- Turning the magnet round so that the south pole goes in first makes the needle swing the other way again, because the field direction has reversed.
- two reversals per revolution of a coil
- A coil spinning steadily in a fixed field gives a potential difference that reverses twice per turn, because each side swaps from moving up through the field to moving down through it.
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