The current magnetises the iron core and creates a pair of magnetic poles, one North, and the other South. The two compass needles consequently point in opposite directions. (You may repeat the experiment by clicking on the switch again).
This magnetic field would be created whether we had the iron core in the middle or not. But the iron core makes the magnetic field much more powerful.
The iron core may be shaped e.g. like a horse shoe, or a C , which is a design used in generators.
Generators usually have several North - South pole pairs.
For now, let's see how electromagnetism can work "in reverse" on the next page on induction.
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Updated 12 May 2003