The Strength of an Electromagnet
AbstractYou 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.
Terik Daly, Andrew Olson, PhD, and Ben Finio, PhD, Science Buddies
Recommended Project Supplies
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).
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:
- Electric current
- Magnetic domains
- How does an electromagnet work?
- Why does an electromagnet have magnetic properties only when energized?
- Does increasing the current flowing through a coil of wire increase or decrease the strength of the magnetic field?
- What does adding an iron core to an electromagnet do to the magnetic field created by the electromagnet?
- Brain, M. and Looper, L. (2006). How electromagnets work. HowStuffWorks. Retrieved May 30, 2012.
- Nave, C.R. (2006). Magnets and electromagnets. HyperPhysics, Department of Physics and Astronomy, Georgia State University. Retrieved May 30, 2012.
- Science Buddies Staff. (2016, August 19). Electricity, Magnetism, & Electromagnetism Tutorial. Retrieved September 14, 2016.
Recommended Project Supplies
- Strength of an Electromagnet Kit, available from our partner
Home Science Tools. Includes:
- 6 volt (V) lantern battery
- Enamel-coated magnet wire, 30 AWG (75 feet)
- Alligator clip leads (2)
- Iron bolts; about 2 1/2 inches long and 1/2 inch in diameter (4)
- You will also need to gather these items, not included in the kit:
- 220 grit sandpaper (about 1 square inch)
- Masking tape (1 roll)
- Box of steel paper clips (about 100 count)
- Scissors or wire cutters
- Optional: Shallow plastic container, slightly longer and wider than the iron bolts
- Recommended: A paper towel holder, or materials to make a simple spool holder for the magnet wire, like a pencil and a small cardboard box
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Making Your Electromagnets
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.
- 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.
- 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.
- Use small pieces of masking tape to attach each end of the coil to the bolt, to prevent it from unraveling.
- 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.
- 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.
- 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.
- Use masking tape and a pen or fine-point marker to label each magnet with the total number of turns.
- 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.
Figure 2. Four electromagnets with 50, 100, 150, and 200 turns of wire, respectively.
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
- Make a data table, like Table 1, in your lab notebook.
|Number of Turns||Number of Paper Clips Picked Up|
- 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.
- Starting with the 50-turn coil, use the electromagnets to pick up paper clips from the shallow container.
- 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.
- 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!
- 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.
- 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.
- 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.
- Count the number of paper clips that the magnet picked up, and record this value in your data table.
- Return all of the paper clips to the container.
Figure 4. Lifting paper clips with the electromagnet.
- Repeat step 3 four more times, for a total of five trials.
- 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.
- Analyze your data.
- Calculate the average number of paper clips picked up for each number of turns in the coil.
- 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.
- 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.
Ask an Expert
- 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.
- 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)
- I am having trouble keeping track of how many turns are in my coil. Do you have any suggestions for tracking that better?
- I am having a hard time keeping my coil neat. Any ideas for keeping my turns tight and lined up nicely?
- The threads on the iron bolts make it hard to keep the turns lined up. Should I worry about this?
- The magnet wire breaks when I try stripping it with sandpaper. How can I stop this?
- How do I know when the wire is stripped?
- My electromagnet is not working. How can I make it work?
- The wire tails of the electromagnet keep falling out of the alligator clips. What can I do about this?
- 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?
- I see sparks when I connect the alligator clips to the coil. Is this something to worry about?
- My electromagnet gets warm and starts to smell. Is this something to worry about?
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.
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.
Ask an Expert
If you like this project, you might enjoy exploring these related careers:
Contact UsIf you have purchased a kit for this project from Science Buddies, we are pleased to answer any question not addressed by the FAQ above.
In your email, please follow these instructions:
- What is your Science Buddies kit order number?
- Please describe how you need help as thoroughly as possible:
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?
Good Question I'm at Experimental Procedure step #7, "Move the magnet back and forth . . ." and the LED is not lighting up.
Bad Question I don't understand the instructions. Help!
Good Question I am purchasing my materials. Can I substitute a 1N34 diode for the 1N25 diode called for in the material list?
Bad Question Can I use a different part?
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