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The Strength of an Electromagnet

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You may be familiar with permanent magnets—the kind that hang on a refrigerator. But did you know that other magnets, called electromagnets, can be turned on and off? When turned on, electromagnets act just like permanent magnets, but if you turn them off, their magnetic properties disappear. Electromagnets are an important part of many electronic devices, like motors, loudspeakers, and hard drives. You can create an electromagnet with a simple coil of wire and a battery. In this project, you will explore whether the strength of an electromagnet changes with the number of turns in the magnet's coil. You will measure the magnet's strength by counting the number of paper clips your electromagnet can lift.


Areas of Science
Time Required
Very Short (≤ 1 day)
Material Availability
A kit is available from our partner Home Science Tools. See the Materials section for details.
Low ($20 - $50)
The electromagnet can become hot during periods of extended use.

Terik Daly, Andrew Olson, PhD, and Ben Finio, PhD, Science Buddies


In this science project, you will make an electromagnet by wrapping a coil of wire around an iron core. You will then investigate whether the number of coils changes the electromagnet's strength.


Electromagnets, or magnets that use the magnetic field created by electrical current flowing through a wire, lie at the heart of many electrical devices, ranging from simple things like doorbells to complex machines like particle accelerators. The strength of electromagnets varies, but some electromagnets are strong enough to lift entire trains! So how does an electromagnet work? How does electric current—the movement of electric charges—make a magnet?

When electric current flows through a wire, it creates a magnetic field. You can prove this to yourself with a magnetic compass (see the Science Buddies Abbreviated Project Idea Using a Magnet as an Electrical Current Detector, and the Electricity, Magnetism, & Electromagnetism Tutorial to learn more). The magnetic field around a straight wire is not very strong. But if the wire is wrapped in a coil, the fields produced in each turn of the coil add up to create a stronger magnetic field. When the coil is wrapped in the shape of a cylinder, it is called a solenoid. When electric current flows through the solenoid, it creates a magnetic field very similar to that of a bar magnet (Figure 1).

Drawing of a magnetic field changing direction in a solenoid based on the direction of an electric current
Figure 1. Illustration of a solenoid and the magnetic field created by the flow of current. Note that if the current changes direction, so does the magnetic field.

If an electromagnet consists only of coiled wire (if it has nothing but air in its middle) then the magnet will not be very strong. But if you place a piece of iron in the middle of the coil—an iron bolt, for example—then the piece of iron, called the core of the electromagnet, will make the magnetic field much stronger. This is because iron is ferromagnetic. It contains lots of tiny areas, called magnetic domains, that act like small magnets. As soon as the iron core is placed in the coil, the magnetic domains line up with the magnetic field made by the solenoid. As a result, the strength of the magnetic field greatly increases.

In this project, you will investigate how the strength of the magnetic field produced by an electromagnet changes as the number of turns in the coil increases.

Terms and Concepts

To do this project, you should do research that enables you to understand the following terms and concepts:



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Experimental Procedure

Making Your Electromagnets

  1. Make four different electromagnets—with 50, 100, 150, and 200 turns of wire, respectively—by tightly winding the magnet wire around the iron bolts (Figure 2). Here are some tips for making the magnets, but you can also refer to our How to Make an Electromagnet video for more details. If you have trouble, see the FAQ for more information.
    1. Use a paper towel holder to hold the magnet wire spool while winding your magnets, or make an improvised one using a pencil and a cardboard box (Figure 3). This will help you keep your coils neat and prevent knots in the wire.
    2. Leave a tail of wire—at least 6 cm long—at each end of the coil. You will use these wire tails to connect the coil to the battery.
    3. Use small pieces of masking tape to attach each end of the coil to the bolt, to prevent it from unraveling.
    4. Rotate the iron bolt to unwind the magnet wire from the spool. Do not pull the wire off the spool and wrap it around the bolt while still holding the bolt; this will cause the wire to get tangled. Use your fingers to keep the wire tight against the bolt, and wrap each successive turn tightly against the previous one. If these instructions are not clear, watch the video to see how to wind the magnet.
    5. Your 50- and 100-turn coils should fit entirely on the smooth part of the bolt. The 150- and 200-turn coils will go onto the threaded part. This will make it more difficult to keep the turns neat and tightly packed against each other, because they will tend to go into the threads of the bolt, but this is okay.
    6. Keep track of how many turns you make. This is easier if you use a piece of tape or a mark on the bolt so you can easily count one full rotation. It also helps to recruit a helper to make tally marks for you.
    7. Use masking tape and a pen or fine-point marker to label each magnet with the total number of turns.
    8. Use the 220-grit sandpaper to sand off 1 cm of the enamel insulation from both ends of each coil. To do this, cut a small piece of sandpaper, fold it in half, then pinch it around the wire and gently pull on the wire several times to remove the insulation. Watch this video for a more detailed explanation of how to strip the wires.
Four metal bolts are wrapped in copper wire each with a different number of wraps
Figure 2. Four electromagnets with 50, 100, 150, and 200 turns of wire, respectively.

A wire spool hangs from a pencil that is pierced through the walls of a cardboard box
Figure 3. An improvised wire spool holder made from a pencil and cardboard box. This makes it much easier to wind the magnets.

Testing Your Electromagnets

  1. Make a data table, like Table 1, in your lab notebook.
Number of Turns Number of Paper Clips Picked Up
1 2 3 4 5 Average
Table 1. Example data table.
  1. Place the paper clips in a small, shallow container. If you do not have a shallow container, put the paperclips in a pile on a flat surface.
  2. Starting with the 50-turn coil, use the electromagnets to pick up paper clips from the shallow container.
    1. Important: Your electromagnets will get hot if you leave them connected to the battery in between tests. Always disconnect one alligator clip when your electromagnets are not in use.
    2. Connect one end of the red alligator clip to the "+" terminal of the battery, and the other end to one end of the wire coil. Make sure you connect to the part where you sanded off the insulation. Note: In electronics, it is standard convention to use red for positive and black for negative. Your electromagnet will still work regardless of which color alligator clip you use, but it is a good habit to practice!
    3. Connect one end of the black alligator clip to the "-" terminal of the battery, and the other end to the free end of the wire coil. As soon as you do this, your electromagnet will turn on and begin to heat up, so it is important to work quickly.
    4. Touch the head of the bolt to the pile of paper clips, and then pull the coil away from the tray (Figure 4). There should be some paper clips attached to the bolt. If it does not lift any paper clips at all, then your electromagnet is not working. See the FAQ for help.
    5. Move the bolt away from the tray, and then disconnect one alligator clip (it does not matter which one, and you do not need to disconnect all four alligator clips). This should turn your electromagnet off and the paper clips should fall away from the bolt.
    6. Count the number of paper clips that the magnet picked up, and record this value in your data table.
    7. Return all of the paper clips to the container.
A small electromagnet presses against paperclips in a bowl

A small electromagnet lifts paperclips

A small electromagnet releases paperclips
Figure 4. Lifting paper clips with the electromagnet.
  1. Repeat step 3 four more times, for a total of five trials.
  2. Repeat steps 3–4 for the 100, 150, and 200-turn coils. Always remember to disconnect your electromagnets from the battery when not in use.
  3. Analyze your data.
    1. Calculate the average number of paper clips picked up for each number of turns in the coil.
    2. Make a graph of the results. Plot the number of paper clips picked up (y-axis) versus the number of turns in the coil (x-axis). If you need help making a graph, try using the Create a Graph website.
    3. Does the number of paper clips picked up increase or decrease as you increase the number of turns in the electromagnet?


For troubleshooting tips, please read our FAQ: The Strength of an Electromagnet.

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  • Try using different metals as core materials inside the coil, such as steel, copper, aluminum, etcetera. You can use nails, bolts, pipe, tubing, and more. For making comparisons, it would be ideal to have core materials that are the same diameter. You can wrap the coils directly around the core materials, as described in the Procedure, or you can make a single coil (for each number of turns that you want to test) and test it with different core materials inside. Here is a procedure for making coils so that you can swap the core material:
    • Make a coil form by wrapping several layers of paper (or a piece of thin cardboard) around a sample of your core material.
    • Use enough layers of paper or cardboard so that the coil form will hold its shape.
    • Tape the paper or cardboard so that it will hold its shape, and then slide it off the cylinder form.
    • Test the coil form with each of the core materials to make sure that they all fit.
    • Wrap your coil around the coil form, as described in the main project Procedure.
    • Now you will be able to slide different core materials in and out of the coil. You can leave the paper form in place.
    • You could also try another experiment to see if removing the paper makes any difference in the strength of the electromagnet. Test the coils both with and without the paper form inside.
    Try comparing the number of paper clips that electromagnets with different core materials can lift.
  • What happens when you change the distance between the coil of wire and a metal core material? For example, increase the diameter of your core forms (described in Variation 1) by 2, 5, 10, and 20 mm.
  • For an interesting addition to your display board, you can map the shape of the magnetic field produced by your electromagnets. Here is how: Mapping Magnetic Fields.
  • What happens when you change the voltage applied across the coil? You can connect two or three lantern batteries in series, or use increasing numbers of D-cell batteries in series. As mentioned before, measure how many paper clips you can lift with a coil at each voltage.

Frequently Asked Questions (FAQ)

If you are having trouble with this project, please read the FAQ below. You may find the answer to your question.
Q: I am having trouble keeping track of how many turns are in my coil. Do you have any suggestions for tracking that better?
A: If keeping track of how many turns of the magnet wire you have made around the iron core becomes difficult, here are two suggestions. First, draw a line straight down the iron core with a permanent marker. Count one turn each time you pass the marker line. Second, each time you add ten turns to your coil, draw a short line on the core next to the wire, and write down how many turns you have so far. If you get distracted, you can unwind to the nearest multiple of ten, instead of unwinding all the way back to the beginning. It is useful to have a helper track how many turns you have made.

Second, if you know the gauge of your magnet wire, you can look up the diameter of the wire in a table, like this one: http://en.wikipedia.org/w/index.php?title=American_wire_gauge&oldid=495948718. Once you know the diameter of the wire, you can calculate how much of the iron core should be covered by a certain number of coils. For example, the wire in the Science Buddies kit is 30 gauge wire and has a 0.01 inch diameter. That means that 100 turns of that wire cover 1 inch of the iron core (0.01 inches x 100 = 1 inch), if the turns are right next to each other and do not overlap. So, if you wrap your coil very neatly, you can estimate how many turns are in your coil by measuring how much of the iron core is covered by the coil. This can be a helpful "reality check," especially if you completely lose count of how many turns you have made in a coil. Note that this method does not work if your coil has more than one layer of wire or if there are spaces between turns.
Q: I am having a hard time keeping my coil neat. Any ideas for keeping my turns tight and lined up nicely?
A: Wrapping the coils is probably the trickiest part of this project, so do not feel bad if you have some trouble with this. But because a neatly wrapped coil is important to the quality of your experiment, it is worth taking the time to wrap your coils well. First, it is important to have the starting point of your coil taped firmly in place to the iron core. (Once you have finished making the turns on your coil, it is also important to tape the ending point of the coil firmly to the iron core. This will keep the coil from coming apart.) Second, you may find it helpful to hold the iron core in one hand and the wire in the other. That way, you can hold the wire taut while you turn the core. Third, you may also find it helpful to use your fingers to hold the wire tight against the iron core as you wrap the coil. Fourth, try using your fingernail to slide each turn of the coil up against the previous turn, while pulling the wire tight with your other hand. If you do this after each turn, your wire turns should line up nicely. Finally, work slowly for best results. A little patience goes a long way in getting a nice coil.
Q: The threads on the iron bolts make it hard to keep the turns lined up. Should I worry about this?
A: We suggest starting your coil as close to the top of the bolt as possible so that you have most of your coil on the non-threaded part of the bolt. The 50- and 100-turn coils should fit completely on the non-threaded section of the bolt. For the 150- and 200-turn coils, you will need to go onto the threaded section of the bolt. This will make it more difficult to keep the turns tightly packed against each other, as they will tend to fall into the threads of the bolt. This is okay, as long as you do your best to continue wrapping at an even pace, and do not bunch up too many turns all in one place.
Q: The magnet wire breaks when I try stripping it with sandpaper. How can I stop this?
A: Try using less pressure. You do not need to squeeze the sandpaper sandwich very tightly in order to remove the enamel insulation that coats the magnet wire. Try practicing on a separate piece of wire to get a feel for how much pressure to apply with the sandpaper. If you did break the magnet wire "tail" of your coil while stripping it, do not worry. You can strip the insulation off the remaining part of the wire tail. You do not need to start over or make a whole new coil, as long as you have enough stripped wire for the alligator clip to hold.
Q: How do I know when the wire is stripped?
A: The wire is stripped when the reddish color of the enamel insulation is gone, revealing bright, shiny, golden-colored copper. The wire will also look a little bit thinner.
Q: My electromagnet is not working. How can I make it work?
A: The electromagnet might not be working for a number of reasons, but most of them boil down to an incomplete circuit. In other words, the electromagnet will not work if something is preventing electric current from flowing from the battery through the wire.

First, check that the electromagnet is correctly connected to the battery. Make sure the alligator clips are connected to both the battery and the wire. One end of each clip lead should be connected to one of the terminals of the battery (one lead to each terminal), and the other end of each lead should be clipped to the stripped part of the magnet wire (one lead to each end of the wire). See Figure 4 in the Procedure. If the clip leads are connected correctly to the coil and battery, but the electromagnet is still not working, then the problem may be that the magnet wire is not completely stripped. Look at the answer to the question "How do I know when the wire is stripped?" and determine if your wire is well-stripped. If not, try re-sanding the ends of the magnet wire until all of the reddish insulation is gone, then reconnect and retest the electromagnet. If the electromagnet is still not working, check to make sure the alligator clips are well-clamped to the stripped part of the magnet wire tails. They should not be clipped to the insulated part of the magnet wire, as insulation prevents electric current from flowing. If the electromagnet still does not work, then the battery may be dead. However, this is unlikely unless you accidentally left one of your electromagnets connected for a very long time and completely drained the battery, which would take hours. Replacement batteries can be ordered from Jameco Electronics.
Q: The wire tails of the electromagnet keep falling out of the alligator clips. What can I do about this?
A: Try putting the wire farther back in the clips, closer to the hinge where you squeeze to open the clip. You can also try stripping the insulation off a longer section of the magnet wire tail and folding over the end of the tail to make it thicker. The alligator clips will hold this thicker section of wire more easily. If you have enough stripped wire, you can also wrap the wire around the tips of the alligator clips.
Q: My finished coils are coming uncoiled because the tape holding the end in place is falling off. Do you have any suggestions for preventing that?
A: Try wrapping a piece of masking tape all the way around the bolt, covering the last part of the coil. As you use the electromagnet, the heat that builds up in the magnet can make the tape brittle, so it is a good idea to apply new tape instead of reusing old tape.
Q: I see sparks when I connect the alligator clips to the coil. Is this something to worry about?
A: No, small sparks are not something to worry about. It is completely normal to see a few small sparks as you connect the alligator clips and complete the circuit.
Q: My electromagnet gets warm and starts to smell. Is this something to worry about?
A: The current running through the circuit will heat up the wire. Whenever you detect a smell, or can feel the electromagnet getting hot, disconnect the electromagnet from the battery. You can reconnect the electromagnet after it cools down.

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    Good Question I'm trying to do Experimental Procedure step #5, "Scrape the insulation from the wire. . ." How do I know when I've scraped enough?
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General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "The Strength of an Electromagnet." Science Buddies, 8 Sep. 2023, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p035/electricity-electronics/strength-of-an-electromagnet. Accessed 14 Apr. 2024.

APA Style

Science Buddies Staff. (2023, September 8). The Strength of an Electromagnet. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p035/electricity-electronics/strength-of-an-electromagnet

Last edit date: 2023-09-08
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