Electricity: Magnetic and Heating Effects
Poles and strength
Test whether an electromagnet has poles, and what makes it stronger.
A bar magnet has a North pole and a South pole. Does an electromagnet?
Test it (Activity 4.4). Label the ends of your coil A and B. Put a compass near end A, switch on, and see which end of the needle is pulled towards A.
Remember: unlike poles attract, North pulls South. So if the compass's North end is pulled towards A, then A must be a South pole. Do the same at B and you find the opposite. Just like a magnet, an electromagnet has two poles, North and South.
What makes it stronger? Repeat Activity 4.3 with 1, 2 and 4 cells, and with different numbers of turns:
| Change | Result |
|---|---|
| more cells (more current) | stronger field: the needle turns more, more clips are picked up |
| more turns of wire | stronger magnet |
| fewer cells or fewer turns | weaker magnet |
So you can change an electromagnet's strength by changing the current, the number of turns, or both. A single cell gives only a small current, so its magnet is weak.
One more control: reverse the current (turn the cell round) and the poles swap. The end that was North becomes South. You can't do that with a bar magnet.
Practise this lesson
Questions that get harder as you improve, a Tutor that helps without giving the answer away, and progress you can see. Free for every learner.
No account, no email address. Opens the real product.