AQA GCSE · Question 08.2 · Magnetism and electromagnetism
Explain why a current was detected when the wire in Figure 13 was moved upwards.
How to approach this question
1. What happens when a conductor (the wire) moves through a magnetic field? Use the phrase "cuts magnetic field lines".
2. What is generated in the wire as a result of this? (Hint: it's not current initially).
3. Why does this generated quantity then lead to a current flowing? What condition must be met?
Full Answer
A current was detected due to the principle of electromagnetic induction.
1. **Cutting Field Lines:** The space between the north and south poles of the magnets contains a magnetic field. When the wire is moved upwards, it moves across and "cuts" through these magnetic field lines.
2. **Inducing a Potential Difference:** Whenever a conductor cuts magnetic field lines, a potential difference (or voltage) is induced across its ends.
3. **Complete Circuit:** The wire is connected to an ammeter, forming a complete closed circuit. This induced potential difference acts like a battery, pushing the free electrons in the wire and causing a current to flow around the circuit, which is then registered by the ammeter.
Common mistakes
✗ Only saying "the wire moved through the magnetic field" without mentioning "cutting" field lines.\n✗ Stating that a current is induced directly, without first mentioning the induced potential difference.\n✗ Forgetting to mention that a complete circuit is necessary for a current to flow.
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