Video: Understanding the Magnetic Field between Two Flat Magnets

Which of the four diagrams correctly shows the field lines of the magnetic field produced by two very wide, flat magnets that are placed near to each other but are aligned in opposite directions? Red represents the north pole of the magnets and blue the south pole.

02:26

Video Transcript

Which of the four diagrams correctly shows the field lines of the magnetic field produced by two very wide flat magnets that are placed near to each other but are aligned in opposite directions? Red represents the north pole of the magnets and blue the south pole.

Looking at the diagrams, we see these four options — a), b), c), and d) — for the correct representation of the field lines of the magnetic field between these two magnets. We may be used to seeing magnets constructed differently than the ones in these diagrams.

We’re told they’re very wide and flat. So whereas we might typically see a magnet that looks like this, these magnets look like a smushed version of that, more like this. We’re told that, with these magnets in the diagram, the red side represents the north pole and the blue side the south pole. We’re also told that these two magnets are aligned in opposite directions, meaning their north poles don’t point the same way but actually point the opposite ways. That fact of being pointed in opposite directions lets us cancel out a few of our answer options.

For example, notice in answer option c) that the north pole, the red part of each of the two magnets, points upward. But since the magnets point in opposite directions, that means this diagram doesn’t represent our scenario. Same thing with answer option b), in this case, the north pole of each of the two magnets points up. So that’s not our answer choice either. That leaves answer options a and d remaining.

If we look more closely at option a, we see that, in this case, we have magnetic field lines which are directed towards the north pole of the two magnets. We can see that from the little arrowheads that are on the field lines, indicating that the field lines go towards the north pole. We can recall that, in reality though, this is opposite the direction that magnetic field lines point. Magnetic field lines always point from the north pole of the magnet to the south pole. That’s true whether we just had one magnet — so the field lines might look like this — or if we had multiple magnets, as we do in this case. So that means option a isn’t our choice either. The field lines in this case point opposite the way they do in real life.

Taking a look at our last option, choice d, we see that, in this case, the south pole of each magnet, indicated in blue, has the field lines pointing toward it. That is an accurate way to represent magnetic field lines pointing from north pole to south pole. Option d shows us two magnets pointed in opposite directions and the field lines are drawn in correctly. So this is our choice for the correct representation of the magnetic field created by these two magnets.

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