Polarity of Electromagnets

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When using electromagnets, pay attention to the fact that there is both a positive and a negative side, with electrons going from minus to plus. Determine the north and south poles of an electromagnet with help from a science teacher in this free video on electromagnets and physics.

Part of the Video Series: Physics & Electromagnetism
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Video Transcript

Hi, I'm Steve Jones, and I'm going to explain how to work out the polarity of an electromagnet. Now, this is our electromagnet, and you can see it is a coil of wire wrapped around some kind of cardboard former. And if you look, this is the actual diagram from the side, this goes up and comes from behind in front, so you can see that it's actually wrapping around the cardboard core in this way, and here, of course, it's going that way. So, this is the positive end. You attach your positive to the battery there, and your minus to the battery there, OK, so, we've got a current flowing through this coil. Now, what I'm got here are two diagrams looking from the end, and if you look from this end you can see that this will be on your left-hand side. The current going down will be on your left-hand side, and the current going up; that one will be on your right-hand side if you just look at it from the end. And this is the view from the opposite end, so we have the views from each end. Now, if the current goes from plus to minus as it does, although it really it doesn't, but we say it does, the electrons go from minus to plus. But here we have, as you can see, the current going round clockwise. And here, the current goes around clockwise, no, anti-clockwise, OK? So, what we will do is we will try and draw a letter N and the letter S, and if we draw an N with the arrows on the extreme sides of it and it goes in the same direction as the arrows on the diagram then we have found a North Pole; that is, this end is a North Pole. But if we draw an S and put arrows on the end of it, and it goes in the same way as the arrows of the current from that view then we have found a South Pole. So, in this way we can identify a South Pole, that it turns out that South Pole is at this end, and a North Pole. It turns out that the North Pole is at this end. So that, basically, is how to determine the polarity of an electromagnet.

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