An electromagnetic switching device contains a moving frame carrying two straight conductor sections, P and Q. The sections are connected in series, so each carries a current of 4.0 A out of the page.
Each section is at right angles to the magnetic field around it.
| conductor section | magnetic flux density | length inside the field | magnetic field direction |
|---|---|---|---|
| P | 0.30 T0.30\ \text{T}0.30 T | 8.0 cm | from left to right |
| Q | 0.20 T0.20\ \text{T}0.20 T | 5.0 cm | from right to left |
Calculate the resultant magnetic force on the moving frame. Include the direction of the resultant force in your answer.
Use the equation
F=B×I×lF = B \times I \times lF=B×I×l
The magnet around section Q is turned round. The current is not changed.
Calculate the new resultant magnetic force on the moving frame. Include the direction of the resultant force in your answer.
The magnet around section Q remains in its new position. The direction of the current through both sections is now reversed, but its size is unchanged.
Explain what happens to the size and direction of the resultant magnetic force on the moving frame.