Video: Understanding Magnetic Interactions

A bar magnet is hung from a thread that is attached to a stand. The magnet can pivot freely. What will happen if the north pole of a second bar magnet is brought near to the north pole of the bar magnet that is hanging from the thread? What will happen if the north pole of the second bar magnet is brought near to the south pole of the bar magnet that is hanging from the thread?

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Video Transcript

A bar magnet is hung from a thread that is attached to a stand. The magnet can pivot freely. What will happen if the north pole of a second bar magnet is brought near to the north pole of the bar magnet that is hanging from the thread? What will happen if the north pole of the second bar magnet is brought near to the south pole of the bar magnet that is hanging from the thread?

Okay, let’s say that this is our bar magnet, this is the thread, and this is the stand that the thread is hanging from. We’ll say that the blue side of our bar magnet is the north pole and the pink side is the south pole. The first part of our question asks this. It says, “What if we take a second bar magnet and we bring the north pole of it near to the north pole of the bar magnet hanging from the thread?”

To figure out what will happen here, it’s helpful to remember that magnetic poles are a bit like electric charge. When it comes to electric charge, like charges repel one another and unlike charges attract. So we would say that positive is drawn to negative but repelled from positive, and negative is drawn to positive but repelled from negative. Well, the same sort of thing happens with magnetic north and south Poles. Unlike poles, a north and a south pole, attract one another, but like poles, for example, the north and north pole we have here, repel one another.

For these bar magnets, because the poles that are closest together are of a like type — they’re both north — that means these magnets will repel one another. If we were to hold this second bar magnet in place so that it couldn’t move, then the one that’s suspended by the string would swing a bit backward. It’s pushed away from the other bar magnet. We can write that out as a sentence this way. We can say that the north pole of the hanging bar magnet will be repelled by the north pole of the second magnet.

In part two of this question, we want to know what will happen if the north pole of the second bar magnet is brought near to the south pole of the bar magnet that is hanging from the thread. In this second scenario then, here’s what we have. We have our second bar magnet. But this time, the north pole of this bar magnet is being brought near to the south pole of the suspended magnet. In this case then, the two poles that are closest to one another, the north and the south poles of these two bar magnets, are of opposite types. Therefore, they’ll attract one another. In this case, the suspended bar magnet will be drawn towards the second bar magnet rather than repelled from it.

Let’s write that out in answer to this second part. Our answer is that the south pole of the hanging bar magnet will be attracted to the north pole of the second magnet. This is what will take place in these two instances of bringing the second bar magnet close to the suspended bar magnet.

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