AQA GCSE PHYSICS · PAPER 2 · FOUNDATION & HIGHER
Induced potential
Magnetism and electromagnetism · Lesson 6 of 8
Teacher copy - includes the notes for whoever is teaching from it.
Warm-up
Answer each one, then check.
1. What does a voltmeter measure?
Potential difference
2. What is a magnetic field?
Region where a force acts on a magnet
3. What is a current?
A flow of charge
4. What is a coil?
Loops of wire
5. What is a conductor?
Allows current to flow
Learning Objectives
1. Describe the generator effect.
2. Describe how a potential difference is induced in a wire or coil by moving a magnet.
3. Explain the direction of the induced current and its effect (Higher).
4. Describe the factors that increase the size of the induced potential difference.
The Generator Effect
The generator effect is when a potential difference is induced across a conductor that moves relative to a magnetic field, or when the magnetic field through a conductor changes. If the conductor is part of a complete circuit, a current is induced.
Nothing is induced if there is no change: a stationary magnet in a stationary coil produces no potential difference.
Inducing a Potential Difference
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No change, no induced potential difference. |
A magnet moving into and out of a coil connected to a meter, showing the induced potential difference changing direction.
What Changes the Induced p.d.
Learn the factors.
|
Change |
Effect on the induced potential difference |
|---|---|
|
Faster movement of the magnet |
Larger |
|
Stronger magnet |
Larger |
|
More turns on the coil |
Larger |
|
Reverse the movement |
Direction of p.d. reverses |
|
Reverse the magnet |
Direction of p.d. reverses |
|
Magnet stationary |
No induced p.d. |
Why Does a Current Flow?
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Explain why a current is produced when a magnet is moved into a coil connected in a circuit. |
1. Magnetic field changes
As the magnet moves in, the field through the coil changes
2. p.d. induced
A potential difference is induced across the coil
3. Complete circuit
The induced p.d. makes a current flow
Answer: A changing field induces a p.d., and a current in a complete circuit.
Direction of the Induced Current
Higher tier.
▸ Its own field. The induced current produces a magnetic field of its own.
▸ Opposes the change. This field opposes the change that produced it.
▸ Energy. You have to do work to push the magnet in.
▸ Conservation. That work is what gets transferred to electrical energy.
Key Terms
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Generator effect The induction of a potential difference across a conductor when the magnetic field changes or the conductor moves in a magnetic field. |
Induced potential difference A p.d. produced by the generator effect. |
|
Induced current A current produced in a complete circuit by an induced p.d. |
Coil Loops of wire. |
|
Flux The magnetic field passing through a coil. |
Galvanometer A sensitive meter that shows small currents. |
Your Task: Magnet in a Coil
12 minutes
|
Push a bar magnet into a coil connected to a galvanometer. Record the deflection: slowly, quickly, out, stationary. What do you notice? 1. Keep the coil the same. |
A good answer shows: Faster gives a bigger deflection; out reverses it; stationary gives zero.
Note: Ask what else would increase the deflection.
Can I...?
☐ State the generator effect.
☐ Say what induces a p.d.
☐ Say when a current flows.
☐ List ways to increase it.
☐ Reverse the direction.
☐ Explain no movement, no p.d.
☐ Explain the opposing field.
☐ Link to energy.
Summary
✓ A changing magnetic field induces a potential difference.
✓ Bigger with faster movement, stronger magnet, more turns.
✓ No movement gives no p.d.
✓ Reversing the movement reverses the p.d.
|
EXAM FOCUS State two ways of increasing the potential difference induced in a coil. (2 marks) Faster movement, stronger magnet, more turns. |
Exam Practice: Induced potential
Answer all questions. Use the mark allocation as a guide to how much to write. · 15 minutes
▸ Question 1 · 2 marks · State. A magnet is pushed into a coil of wire connected to a voltmeter. State two ways of increasing the reading on the voltmeter.
▸ Question 2 · 3 marks · Explain. A student holds a bar magnet still inside a coil of wire connected to a voltmeter. The voltmeter reads zero. Explain why and what they…
▸ Question 3 · 3 marks · Describe. Describe what happens to the reading on the voltmeter when the magnet is pulled out of the coil at the same speed as it was pushed in.
▸ Question 4 · 3 marks · Explain. Explain why a current flows when a magnet is moved into a coil that is part of a complete circuit.
▸ Question 5 · 3 marks · Explain. Explain why it is harder to push a magnet into a coil connected in a complete circuit than into a coil that is not connected.
Question 1 · 2 marks · State
|
“A magnet is pushed into a coil of wire connected to a voltmeter. State two ways of increasing the reading on the voltmeter.” |
HOW TO ANSWER IT Command word: State. Worth 2 marks, so plan before writing.
Question 1 · mark scheme
2 marks available. Award a mark for each point made.
▸ One way. 1 mark
▸ Another way. 1 mark
▸ Model answer. Move the magnet faster. Use a stronger magnet. Use more turns on the coil. (any two)
Question 2 · 3 marks · Explain
|
“A student holds a bar magnet still inside a coil of wire connected to a voltmeter. The voltmeter reads zero. Explain why and what they should do to get a reading.” |
HOW TO ANSWER IT Command word: Explain. Worth 3 marks, so plan before writing.
Question 2 · mark scheme
3 marks available. Award a mark for each point made.
▸ No change in field. 1 mark
▸ No p.d. induced. 1 mark
▸ Move the magnet. 1 mark
▸ Model answer. There is no change in the magnetic field through the coil so no potential difference is induced. They should move the magnet in or out of the coil.
Question 3 · 3 marks · Describe
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“Describe what happens to the reading on the voltmeter when the magnet is pulled out of the coil at the same speed as it was pushed in.” |
HOW TO ANSWER IT Command word: Describe. Worth 3 marks, so plan before writing.
Question 3 · mark scheme
3 marks available. Award a mark for each point made.
▸ A reading is shown. 1 mark
▸ Same size. 1 mark
▸ Opposite direction. 1 mark
▸ Model answer. The voltmeter shows a reading of the same size but in the opposite direction (reversed polarity).
Question 4 · 3 marks · Explain
|
“Explain why a current flows when a magnet is moved into a coil that is part of a complete circuit.” |
HOW TO ANSWER IT Command word: Explain. Worth 3 marks, so plan before writing.
Question 4 · mark scheme
3 marks available. Award a mark for each point made.
▸ Changing field through the coil. 1 mark
▸ p.d. induced. 1 mark
▸ Complete circuit so current flows. 1 mark
▸ Model answer. The movement of the magnet changes the field through the coil, which induces a potential difference. Because the circuit is complete, the p.d. makes a current flow.
Question 5 · 3 marks · Explain
|
“Explain why it is harder to push a magnet into a coil connected in a complete circuit than into a coil that is not connected.” |
HOW TO ANSWER IT Command word: Explain. Worth 3 marks, so plan before writing.
Question 5 · mark scheme
3 marks available. Award a mark for each point made.
▸ Induced current produces its own field. 1 mark
▸ Opposes the motion. 1 mark
▸ Work done is transferred to electrical energy. 1 mark
▸ Model answer. The induced current produces a magnetic field that opposes the change (the magnet's motion), so work must be done to push the magnet in. That work is transferred to electrical energy. With no complete circuit there is no current and so no opposing force.