A student builds a large model of a moving-coil microphone. The coil is attached to a card diaphragm and is connected in a complete circuit to a sensitive ammeter. A motor moves the diaphragm at a steady speed, so the coil moves at the same speed and in the same direction.
The same magnet and circuit are used throughout, but the magnet is turned round between some tests. The resistance of the circuit does not change. A positive reading means that the current enters the positive terminal of the ammeter.
The table shows the results. The direction of movement was not recorded for Test 2.
| Test | Direction of coil movement | Speed of coil in m/s | Pole of magnet nearer the front of the model | Current reading in mA |
|---|---|---|---|---|
| 1 | towards the front | 0.12 | north | +0.30 |
| 2 | not recorded | 0.12 | south | +0.30 |
| 3 | away from the front | 0.24 | south | +0.60 |
Explain which direction the coil was moving in Test 2.
For Test 4, the student moves the coil towards the front at 0.24 m/s, with the south pole nearer the front. Explain what current reading the ammeter would show.
96 exam-style questions on AQA GCSE Physics 7.3 Induced potential, transformers and the National Grid (HT only), covering 7.3.1 Induced potential (HT only), 7.3.2 Uses of the generator effect (HT only), 7.3.3 Microphones (HT only), and 7.3.4 Transformers (HT only). Each one has a worked solution and a mark scheme showing where the marks go.