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.
