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The Strength of an Electromagnet

Difficulty
Time Required Short (2-5 days)
Prerequisites None
Material Availability Readily available
Cost Low ($20 - $50)
Safety The electromagnet can become hot during periods of extended use.

Abstract

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 science fair project idea, 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.

Objective

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.

Credits

Terik Daly and Andrew Olson, Ph.D., Science Buddies

Cite This Page

MLA Style

Science Buddies Staff. "The Strength of an Electromagnet" Science Buddies. Science Buddies, 30 June 2014. Web. 23 July 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p035.shtml>

APA Style

Science Buddies Staff. (2014, June 30). The Strength of an Electromagnet. Retrieved July 23, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p035.shtml

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Last edit date: 2014-06-30

Introduction

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). 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. (See Figure 1)

Magnetic field lines of a magnetic coil.
Electronics Science science project
Figure 1. The green lines show the magnetic field surrounding a solenoid (or cylindrical coil) through which electric current is flowing. "N" and "S" indicate the north and south poles of the electromagnet.

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 magnetic core or iron core of the electromagnet, will make the magnetic field much stronger (see Figure 2). 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 coiled wire solenoid. As a result, the strength of the magnetic field around the solenoid greatly increases.

Electromagnet science fair project: diagram of an electromagnet
Electronics Science science project
Figure 2. Insulated wire (blue) wrapped around an iron core (black). Electric current flowing through the wire creates a magnetic field, a field that is magnified by the iron core.

In this science 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:

  • Electromagnet
  • Electric current
  • Solenoid
  • Iron core
  • Ferromagnetic
  • Magnetic domains

Questions

  • 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?

Bibliography

Materials and Equipment Product Kit Available

These specialty items can be purchased from the Science Buddies Store:

  • The Strength of an Electromagnet kit (1). Includes:
    • 6 volt (V) lantern battery
    • Enamel-coated magnet wire, 30 AWG (75 feet)
    • Alligator clip leads (2)
    • Iron bolts; about 2 ½ inches long and ½ inch in diameter (4)

You will also need to gather these items:

  • 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

Order Product Supplies

Buy Kit
Project Kit: $24.95

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Experimental Procedure

Note Before Beginning: This science fair project requires you to hook up one or more devices in an electrical circuit. Basic help can be found in the Electronics Primer. However, if you do not have experience in putting together electrical circuits you may find it helpful to have someone who can answer questions and help you troubleshoot if your project is not working. A science teacher or parent may be a good resource. If you need to find another mentor, try asking a local electrician, electrical engineer, or person whose hobbies involve building things like model airplanes, trains, or cars. You may also need to work your way up to this project by starting with an electronics project that has a lower level of difficulty.
  1. Make four different electromagnets, using four identical iron or galvanized steel bolts. The first electromagnet will have 50 turns in its coil, the second will have 100 turns, the third will have 150 turns, and the fourth will have 200 turns. It is important to wrap the magnet wire neatly around the bolts. Here are some tips to make wrapping easier.
    1. Leave a tail of wire (5-6 centimeters [cm] long) at each end of the coil. You will use these wire tails to connect the coil to the battery.
    2. Make a holder for the spool of magnet wire, so you can roll the wire right off the spool. For example, you can stick a pen or pencil through the spool, and tape the pencil to a couple of small boxes.
      1. Use a small piece of masking tape to attach the wire to the iron bolt, near where the head of the bolt connects to the shaft of the bolt.
      2. Turn the iron bolt to unwind the magnet wire from the spool. Use your fingers to keep the wire tight against the bolt. Wrap each successive turn so that the wire lines up neatly.
        1. Note: How neatly you coil the wire will affect the strength of your electromagnet, so take the time to coil the wire neatly. See Figure 2 above for an example of what neatly coiled wire should look like: the turns of wire are tight against the iron bolt, and the turns lie next to each other, with no empty space between them.
      3. Keep track of how many turns you make (or how many times you wrap the wire around the bolt). A turn happens each time the tape that holds the wire in place comes around. Counting turns is easier if you can recruit a helper to make tally marks for you.
        1. Troubleshooting Tip: If you are having trouble keeping track of how many turns you have made, here are two tips.
          • First, draw a line straight down the iron core using a permanent marker. Count one turn each time you pass that line.
          • 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 for American wire gauge. Once you know the wire's diameter, you can calculate how much of the bolt should be covered by a given 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 cover 1 inch of the bolt (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 get a rough idea of how many turns are in your coil by measuring how much of the bolt is covered by the 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.
      4. When you reach the desired number of turns, tape the wire to the bolt to hold the coil in place. Cut the wire, leaving a 5-6 cm long "tail" for making the connection to the battery.
      5. Particularly for larger coils, you may need to wrap multiple layers of wire, one layer on the other, to get the desired number of turns.
    3. Use the 220 grit sandpaper to sand off 1 cm of the enamel insulation from the end of each magnet wire tail. You will need to do this for all four of your electromagnets.
      1. Fold a small piece of sandpaper (about the size of two postages stamps, use scissors to cut a small piece of necessary) in half, with the rough sides facing each other, to make a "sandpaper sandwich".
      2. Put the end of the magnet wire to be stripped inside the sandpaper sandwich.
      3. While softly pressing the sandpaper sandwich together, gently pull the wire through the sandpaper sandwich, turning the wire as you pull so that you remove the insulation from all sides of the wire. Or, you can rub the wire back and forth inside the sandpaper sandwich.
      4. The wire is stripped when you can see the shiny copper wire underneath.
        1. Troubleshooting Tip: It is a good idea to practice stripping the enamel insulation off a practice piece of wire. You may need some practice to get the pressure right so that the wire does not break while you sand it.
    4. Place the paper clips in a shallow container (slightly longer and wider than the electromagnet). If you do not have a shallow container, put the paperclips in a pile on a flat surface.
    5. Starting with the 50-turn coil, use the electromagnet to pick up paper clips from the shallow container.
      1. Use the alligator clip leads to connect the coil to the battery. When current flows through the coil, the coil is energized and will behave as a magnet. When no current flows through the coil, the magnetic characteristics of the electromagnet disappear.
        1. Troubleshooting Tip: After connecting the coil to the battery, you can check that the electromagnet works by touching a paper clip to the coil. If the paper clip sticks, then the electromagnet is working. If the paper clip does not stick, then the electromagnet is not working. If this is the case, make sure that the alligator clips are connected to both the battery and the wire. One end of each lead should be clipped to one of the terminals of the battery (one lead to each terminal), and the other end of each of lead should be clipped to the stripped part of the magnet wire (one lead to each end of the wire). 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 was not completely stripped. Try re-sanding the ends of the magnet wire until all of the reddish insulation is gone, then reconnect and retest the electromagnet.
      2. Touch the energized coil (lengthwise) to the paper clips, and then pull the coil away from the tray. See Figures 3 and 4.
        Electromagnet science fair project idea: electromagnet picking up objects
Electronics Science science project
        Figure 3. After connecting the alligator clip leads to the battery and wire on the coil, the electromagnet will be energized. Lower the electromagnet into the container of paper clips so that the long part of the electromagnet touches the paper clips.

        Electromagnet physics electricity science fair project idea: electromagnet with paper clips
Electronics Science science project
        Figure 4. Once you have touched the electromagnet to the paper clips, lift the electromagnet up. Some of the paper clips will stick to the electromagnet. Move the electromagnet away from the container (so that the paper clips will not fall back into the container) and then disconnect the coil from the battery.

      3. Once the coil is no longer over the container, disconnect the coil from the battery, and count how many paper clips the coil picked up. Record the number in your lab notebook. Organize your data in a table like Table 1.
      4. Repeat steps 4a to 4c four more times, for a total of five trials.
    6. Repeat step 4 for the 100-, 150-, and 200-turn coils.
    7. Calculate the average number of paper clips lifted by each coil (see Table 1).
    Number of Turns on Coils Number of Paper Clips Picked Up
    1 2 3 4 5 Average
    50            
    100            
    150            
    200            

    Table 1. Record the number of paper clips each coil picked up in each of the five trials and then calculate the average for the five trials.

    Analyzing the Data

    1. Make a graph of the results. Plot the number of turns in the coil (x-axis) versus the number of paper clips picked up (y-axis).
    2. Does the number of paper clips picked up by the coil increase or decrease as you increase the number of turns in the electromagnet?

    Troubleshooting

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

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    Variations

    • Try using different metals as core materials inside the coil, such as steel, copper, aluminum, etc. You can use nails, bolts, pipe, tubing, etc. For making comparisons, it would be ideal to have core materials that are the same diameter and weight. You can wrap the coils directly around the core materials as described above, 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 above.
      • 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.
      As in the procedure above, you can compare 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, above) 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's how: Mapping Magnetic Fields.
    • What happens when you change the voltage applied across the coil? You can connect two or three lantern batteries in a series, or use increasing numbers of D-cell batteries in a series. As above, measure how many paper clips you can lift with a coil at each voltage.

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    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 larger coils, you have a couple of options. First, you can ignore the threads and keep on wrapping, even though it will be harder to keep the turns lined up because the wire will tend to lie in the threads of the bolt. Second, when you reach the threads, you can start wrapping the coil in the other direction, away from the threads and on top of the first set of turns, creating a second layer to your coil. Either option gives good results.
    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 1. 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 question 5 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. Try replacing the battery with a new one.

    Connect the electromagnet coil to the battery using two alligator clips.
    Figure 1. Connect the electromagnet coil to the battery using two alligator clips. Clip one lead of each alligator clip to each of the battery terminals. Then clamp the second lead of each alligator clip to the stripped part of the wire tails, one lead to each tail, as shown here.
    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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    If 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:
    1. What is your Science Buddies kit order number?
    2. Please describe how you need help as thoroughly as possible:

      Examples

      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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      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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