An electromagnetic valve contains a coil. A spring closes the valve unless the magnetic field from the coil is strong enough to hold it open.
The current through the coil is kept the same for both measurements. The magnetic flux density is measured at the moving part of the valve.
| Core in the coil | Magnetic flux density in mT |
|---|---|
| No core | 2.1 |
| Iron core | 9.4 |
Tests show that the valve remains open only when the magnetic flux density at the moving part is at least 8.0 mT8.0\ \text{mT}8.0 mT.
Use the data to explain why inserting the iron core allows the valve to remain open.
Predict what happens to the valve when the current is switched off. Explain your answer.
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.