A motor opens a small valve in an irrigation pipe. An engineer measures the turning effect produced by coils wound on the same former and placed between the same magnets. For each measurement, the coil is held at the same angle.
| Test | Number of turns | Current / A\mathrm{A}A | Turning effect / mN m\mathrm{mN\,m}mNm |
|---|---|---|---|
| A | 12 | 0.50 | 2.4 |
| B | 24 | 0.50 | 4.8 |
| C | 24 | 0.75 | 7.2 |
Describe the pattern shown by the results.
The valve needs a turning effect of at least 5.2 mN m to open. A replacement coil on the same former has 18 turns and can carry a maximum current of 0.70 A.
Calculate the greatest turning effect of the replacement coil and state whether it will open the valve.
86 exam-style questions on Edexcel GCSE Physics 12.3 The motor effect, covering 12.3.1 The motor effect, 12.3.2 Fleming's left-hand rule, 12.3.3 Force on a conductor, and 12.3.4 Electric motors. Each one has a worked solution and a mark scheme showing where the marks go.