An electrically operated bolt contains a permanent magnet attached to a sliding rod. A fixed straight conductor passes through the gap between the poles of the magnet, at right angles to the magnetic field.
The bolt is released only when the magnetic force on the magnet is at least 0.10 N to the left.
In a modified design, the magnet has narrower pole faces but the same magnetic flux density in the gap.
| Design | Current | Current direction | Length of conductor inside the field | Force on the conductor |
|---|---|---|---|---|
| Initial | 4.0 A | original | 0.050 m | 0.12 N to the right |
| Modified | 6.0 A | reversed | 0.040 m | not measured |
Calculate the magnetic flux density in the gap.
Calculate the size of the magnetic force on the conductor in the modified design.
Explain whether the bolt is released in the modified design.
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.