The strength of the magnetic field produced by an electromagnet depends on a lot of variables. We're going to experiment with a few different electromagnet configurations and measure the field strength to get an idea of how it changes.

To begin, we'll make an approximately 2 inch diameter coil of wire. The size isn't that important, as long as the digital compass can sit flat inside it. You can wrap each end around the coil to keep it together.

Then, using a razor knife, strip the enamel off the ends of the wire. It doesn't need to be much, just enough for the alligator clips to get a good connection. It's easiest if you lay the wire on the edge of a table and scrape the enamel. Then rotate it a bit and repeat until it's bright copper.

In the next section we'll use a digital compass attached to one of the I2C pins of the Arduino. If you haven't already, attach the compass to the Arduino and connect the Arduino to the computer.

In this section we're going to take some readings of the field strength. To begin, we should measure the field without power applied to the coil. Place the compass flat inside the coil. Notice that if you turn the compass or move it on the table the readings will change. This is because the compass is quite sensitive and is reacting to the Earth's magnetic field.

Attach the red alligator clip wire to the red wire of the battery holder and the black alligator clip wire to the black side. Then clip the other end of each wire to different ends of the coil. Try to keep the coil and compass still while you do this, and watch the readings from the compass. What do you notice? Now, place the compass flat on the table, but just outside the coil. What's different?

Next, disconnect the alligator clips from the coil and swap them so that the red wire is connected to the end of the coil the black wire was on. Take another reading with the compass inside and outside the coil. Are the measurements different than they were when the alligator clips were attached the other way?

In the last section you should've noticed the Z axis change a lot when the power was applied. Depending on which way you connect the battery to the coil, the Z axis will either increase or decrease. You should've also noticed that the field outside the coil did the opposite of the field inside, but a lot weaker. That means that if you saw a large increase in the Z axis inside the coil, you should see a small decrease outside. Another thing to notice is how weak the change is. It's kind of hard to tell just by looking at milligauss, but the coil is only a very weak electromagnet.

Next we'll use a nail as a metal core for an electromagnet. This greatly increases the strength, but it's not very easy to measure inside the coil! Instead we'll measure at the end and next to it. Start by unwinding the large coil. Then start winding the wire around the nail starting near the head. Make sure to leave the stripped part unwound - we'll need to attach a clip to it. Only wrap about half to begin with.

Line up the nail so it points along on the the axes of the compass. Then clip the power to both ends. You might need help holding it all steady while you do this. The magnetic field near the end of the coil is kind of messy, so you might need to move the nail a little bit to get the highest reading.

Then measure alongside the nail. Place the compass so the nail is parallel to one axis. Then apply the power again and watch the readings. Do you notice any similarities between this and the larger coil?

Now wrap the whole nail, and take the same measurements. What differences do you notice?

Based on the measurements you've taken, what variables do you think influence the strength of the magnetic field? Design a different configuration for an electromagnet and test it the same way.