A control unit contains a straight cable carrying a current. A magnetic sensor can be fitted at position P, Q or R near the cable. The sensor gives less reliable readings when the magnetic field from the cable is stronger.
A field-line representation of the magnetic field uses the same scale and convention at all three positions. The table gives measurements taken from this representation.
| Position | Separation between neighbouring field lines in the representation |
|---|---|
| P | 2.0 mm |
| Q | 4.5 mm |
| R | 7.0 mm |
Which position should be used for the sensor? Explain your answer using the data.
The current in the cable is then increased. What happens to the strength of the magnetic field at the chosen position?
90 exam-style questions on AQA GCSE Physics 7.2 The motor effect, covering 7.2.1 Electromagnetism, 7.2.2 Fleming's left-hand rule (HT only), 7.2.3 Electric motors (HT only), and 7.2.4 Loudspeakers (HT only). Each one has a worked solution and a mark scheme showing where the marks go.