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A bar magnet lies on a table with its north pole to the east…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A bar magnet lies on a table with its north pole to the east. Ignore the Earth's field. Which way does the north end of a small compass point when the compass is
- just east of the north pole, on the line of the magnet?
- beside the middle of the magnet, a little to the north of it?
Need a reminder? The key ideaShow
Field lines run from the north pole to the south pole outside a magnet, and back inside it, so they are closed loops. The field is strongest where the lines are closest together. Two lines never cross. A compass's north end points along the line through it.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) On the line of the magnet, the field points away from the north pole. The north end of the needle points east, away from the magnet.
Step 2. (b) Beside the middle, the lines run parallel to the magnet, from the north end toward the south end. The north pole of the magnet is to the east, so the needle points west.
Answer: (a) east, away from the magnet. (b) west, parallel to the magnet.
Check. In (b) the needle's north end is pushed away from the magnet's north pole and pulled toward its south pole: both pushes point west.
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