What Makes A Compass Needle Move?

Compass deflection



A Fourth Grade Science Project: Compass Deflection

Does a compass always have to point North?  If not, why not?

What if we propose that it points in the direction of the stronger magnetic field?  How could we prove that?

Earth’s magnetic field is certainly there, but as we saw in the magnetic science projects page, electricity and magnetism are definitely related.  So, if we have a stronger magnetic field than that of the Earth’s, might we be able to deflect what a compass needle will show as North?

And what about the magnetic field induced from current flowing through a wire.  Is any of that related?

Hmmm … let’s see …



This fourth grade science project is designed to introduce young students to the concept of magnetism by using everyday items they are most likely already familiar with.  In this project, we will show that a compass does not always have to point North. Instead, it will point in the direction of a stronger magnetic field.  And, as we will soon see, the flow of current through a wire will deflect the compass needle, which means something magnetic must be going on there as well …


Materials Needed

Recommend groups of 3 to 5.
You will need the following for each lab station:
Project Supplies

The photo on the right shows the fourth grade science project kit for several experiments, but you will only need the following from that:

  • About a 1 Ft section of the insulated wire
  • 1 D cell battery
  • 1 Compass
  • 1 Magnet (any size will do)



For this project … just remove about 1” of insulation from each end of the insulated wire sections.

That’s it. Now it’s time to have fun …


Project Day

Before anybody gets the material out, we need to discuss a couple fourth grade science project safety items. First, we will be working with batteries. Yes, they are the same ones they use at home in flashlights, games, radios, etc. The difference here is that they will not be in a protective cover. Also, we will be hooking them up with wires. That does several things:

– The batteries will run down quickly if the wires are left on too long
– The batteries will get hot if left connected too long
– The wire will get hot if connected too long
– Rare, but a battery could rupture if connected too long

No panics here … just please insist they wear the safety glasses.

Then tell’em all to have fun with the experiment, but if the wire starts to get hot, disconnect it from the battery and wait a minute or two before continuing.

Now let’s get started …


Compass Deflection

Have the students take the battery, the 1 Ft section of insulated wire and the compass out. Show them where North is, and mention that the compass should point there now. You might need to explain that a compass is really just a magnet, so it will also point toward metal, like screws and braces under the desk top. Have them move the compass around until it points as close to North as possible. This just gives them a reference point to start with.

Mention again about the wire getting hot if connected to the battery too long, then demonstrate how to hold the wire ends on the battery to complete an electric circuit. You can use a rubber band to keep the wire connected if desired.

Tell them that the current flows from the positive terminal (the one with a + sign by it) to the negative terminal. As the current flows in the wire, a magnetic field is created around it. We can see that in our fourth grade science project by watching the compass needle as we move it close to the wire.

Have one student in each group connect the wire ends to the battery, while another moves the compass around. If you have a fairly advanced class, tell to put their thumb in the direction of the current (thumb pointing away from the positive terminal). If their fingers are straight out when doing that, they will be pointing in the direction the North end of the compass will point.

Then explain that the magnetic field really goes all the way around the wire, and if they curl their fingers while keeping the thumb pointed in the direction of the current, they can see what that means as well. (If they are having trouble grasping the concept today … just leave this part out till next year!)

Have them move the compass around the wire to show that the magnetic field really does “push” the compass needle straight away from the wire all the way around. At some point, have them disconnect the battery to see what happens. They should see the needle point back toward North.

The photo below shows what they should see.

Simple Electromagnet

Repeat the process with only the compass and the magnet.  They should see that the needle of the compass will move with the magnet as well.


So What Just Happened?

For the teacher – A magnetic field can be created by current (electrons moving through our wire), or by a magnet itself.

In either case, the compass needle will follow the stronger magnetic field, be that the magnet, the magnetic field induced by current through the wire, or the earth itself.  If only the earth’s magnetic field is involved, the the compass points to (magnetic) north. But, if we have a stronger magnetic field close to the compass, that may not be the case!

For the students – we can make a compass tell us “North” isn’t really North by simply putting a magnet, or a magnetic field close to it.  So, we need to make sure we know what is the “driving force” on the compass before we rely on it to give us directions!

… and for a more “out of the box” type projects for Magnetic Science Experiments, the following should help …







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