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Build a temporary electromagnet by winding several hundred turns of 28 AWG enamel-coated wire around a magnetic iron or steel core, then connecting the coil briefly to a 6 V battery. Use a compass to identify its poles and a small permanent magnet to test attraction and repulsion. Keep each battery connection brief: the coil can heat up, a direct short can damage the battery, and interrupting current can create a spark.
What this experiment demonstrates
An electromagnet is a magnet produced by electric current. Current flowing through a wire creates a magnetic field; winding the wire into a coil makes the fields from its turns reinforce one another. A ferromagnetic core, such as soft iron, concentrates the field. When current stops, the powered field disappears, though a steel core may retain some magnetism.
The coil’s polarity depends on the direction of current and the way the wire is wound. Reversing the battery connections reverses the electromagnet’s north and south ends. More turns can increase the field, but extra wire also adds resistance, which can reduce current. Strength therefore depends on turns, current, coil geometry, core material and heating—not voltage alone. Florida State University’s Magnet Academy explains how coils and magnetic cores produce electromagnets.
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| Item | Specification | Purpose and notes |
|---|---|---|
| Battery | 6 V for the referenced build | Supplies current for short tests. Battery chemistry, condition and internal resistance affect the result. |
| Magnet wire | 28 AWG, enamel-coated copper; several hundred turns | Enamel insulates adjacent turns. Remove it from the two ends before connecting the coil. |
| Core | Magnetic iron or steel nail, bolt or rod | Soft iron is preferred; ordinary magnetic steel can work but may retain magnetism. Check the core with a permanent magnet before winding. |
| Compass | Small magnetic compass | Shows the field direction near each end of the energized core. |
| Permanent magnet | Small bar or disc magnet | Used to compare attraction and repulsion after identifying the coil’s poles. |
| Electrical tape | Standard insulating tape | Protects the wire from abrasion and holds the winding in place. |
| Connection hardware | Insulated alligator clips and a momentary switch are recommended | Makes brief connections easier without holding bare wire against the battery. Do not use the hardware to short the battery. |
| Small test objects | Paper clips or staples | Provide a rough demonstration of attraction, not a calibrated measurement of magnetic strength. |
Metal alone does not make a suitable core. Aluminum, brass, copper and plastic are not substitutes for magnetic iron or steel. Some stainless-steel fasteners are nonmagnetic, so test a candidate with a permanent magnet first. The referenced build uses a 6 V battery, 28-gauge magnet wire, a magnetic core, a compass and a permanent magnet.
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Safety before you build
- Use brief, supervised battery connections; there is no specified safe continuous run time for this build. Disconnect promptly after each observation.
- Never connect the battery terminals directly together. A low-voltage battery can still deliver enough current into a short to heat conductors, damage the battery or cause burns.
- Stop immediately if the wire, core, switch or battery becomes hot. Disconnect, let everything cool, and inspect the winding and connections before deciding whether to continue.
- Keep fingers away from the connection as you open the circuit. A collapsing magnetic field can produce inductive kickback: a voltage spike that may cause a spark. Use insulated switching hardware; one-hand operation is not a guarantee of safety.
- Do not substitute a mains-powered supply. An advanced experimenter using a bench supply should use an appropriate current limit and supervision.
- Keep magnets away from sensitive electronics and magnetic media. Move steel tools and other magnets away from the compass during pole measurements.
- Children should work with adult or instructor supervision. Eye protection is sensible, especially when scraping enamel or handling cut wire ends.
Classroom guidance also warns that a nail or wire can become hot and should be disconnected if it does. The University of Alaska Geophysical Institute’s classroom activity uses a 6 V setup and discusses coil-count comparisons, but its particular results are not a universal performance specification. For connection safety, Simon Fraser University’s demonstration guidance recommends sheathed clips and warns against prolonged battery shorts.
Wind the coil
- Wrap one layer of electrical tape around the core to reduce abrasion. Leave a generous free lead at both ends of the wire.
- Wind the enamel-coated wire around the core in one continuous direction. Make several hundred reasonably tight, adjacent turns; a neat single layer is helpful, but overlapping turns are acceptable for this demonstration.
- Do not reverse the winding direction midway. Secure the completed coil with one or two layers of tape, leaving the two wire leads accessible.
- Scrape or sand the enamel from all around the final section of each lead until clean copper is visible. Do not strip insulation along the working length of the coil.
- Inspect the coil for broken wire, damaged enamel, or bare turns that touch the core or one another. Replace damaged wire rather than testing a suspect winding.
Hand winding is the practical default. A powered winding method is optional, not necessary; it requires a secure setup, slow speed, controlled wire feed, eye protection and a clear stop procedure, and is inappropriate for unsupervised beginners.
Connect the battery and confirm attraction
Connect the battery and coil in series, so current flows from one battery terminal through the coil and back to the other terminal. A momentary switch or insulated clips make it easier to energize the coil only while testing.
- Check that both coil ends are clean bare copper and that the battery is not damaged.
- Connect one coil end to the battery’s negative terminal.
- Make the other connection to the positive terminal only for a brief test. Release the switch or connection as soon as you have observed the response.
- Bring a paper clip or staple near the core while current is flowing. Note whether it is attracted, then disconnect.
If you use clips, connect each clip to a coil lead and use the switch to control current; do not bridge the battery terminals. A simple schematic is battery terminal → coil → switch → other battery terminal, with all components in one series loop.
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The number of clips lifted can be recorded for a rough comparison, but it is not a precise field-strength measurement: clip size, contact, battery condition, coil resistance and test duration all affect the outcome. Do not leave the coil connected between observations. TeachEngineering’s classroom activity likewise treats battery-and-coil tests as comparisons and warns about current and heating.
Identify the poles with a compass
- Move the permanent magnet, steel tools and other magnetic objects away from the compass.
- Energize the coil briefly and bring the compass near one end of the core without touching the connection.
- Wait for the needle to settle. Use the compass’s marked north-seeking end and the known compass orientation to determine the field direction at that end. The end of the electromagnet toward which the compass’s north-seeking end points is its south pole; the compass needle’s north end points toward a magnetic south pole.
- Repeat at the opposite end. Label the two ends, then disconnect the coil.
Nearby magnets or steel can distort the reading. If the needle does not settle consistently, increase the separation from those objects and repeat. The original experiment’s compass and permanent-magnet checks are described in the All About Circuits lab instructions.
Test attraction, repulsion and reversed current
- With the coil energized briefly, bring one pole of the permanent magnet near one labeled end of the electromagnet. Record whether they attract or repel.
- Turn the permanent magnet around so its opposite pole faces the same electromagnet end. Repeat and record the change.
- Disconnect the battery, reverse the two battery connections, then repeat the test with the permanent magnet in the same orientation.
Turning the permanent magnet changes the pole presented to the coil; swapping battery connections reverses the coil’s polarity. Keep those changes separate in your notes so you can tell which one caused the observed change in force.
Make the build a controlled experiment
Change one variable at a time and keep the rest of the setup as constant as practical. Compare the same test objects at the same distance, use the same core and measurement method, and keep test duration brief and consistent. Record battery condition because a weak or aging battery can make a sound coil appear weak.
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- Turns: Compare different turn counts while keeping the core, battery, test object and test duration the same. The Alaska activity reports roughly 80 wraps with a 6 V battery as stronger than a lower-wrap comparison in its lesson setup; that result is specific to that setup, not a universal target.
- Core: Compare magnetic iron or steel with a nonmagnetic core of similar dimensions. The nonmagnetic core will not concentrate the field in the same way.
- Current and battery: A higher voltage may raise current and field strength, but can also increase heating and battery stress. Do not treat higher voltage as automatically better.
- Wire and geometry: Finer wire can fit more turns into a given space; thicker wire generally allows more current but occupies more space. The balance depends on resistance, current, turns and heat. A compact, orderly winding is easier to compare than a loose bundle.
- Residual magnetism: Check whether the core still attracts a small object after disconnection. Steel may retain more magnetism than soft iron.
Use this record sheet for repeatable observations:
| Trial | Turns | Core material and size | Battery condition | Test duration | Objects attracted or lifted | Warmth observed | Pole direction |
|---|---|---|---|---|---|---|---|
| 1 | |||||||
| 2 | |||||||
| 3 |
Troubleshooting
No attraction
- Test the core with a permanent magnet; if it is nonmagnetic, choose an iron or magnetic-steel core.
- Check that both wire ends are fully stripped to clean copper and that the clips or switch actually contact the bare metal.
- Inspect for a broken lead or damaged winding, then confirm that current is flowing only during the test.
- Try a known ferromagnetic test object and check the battery condition.
Weak attraction
Check for too few turns, loose or widely spaced winding, a weak battery, poor connections or an unsuitable core. Test with a lighter ferromagnetic object and keep its position consistent. Do not respond by simply increasing voltage: that may increase current and heat without producing a safe or useful comparison.
Coil or battery gets warm
Disconnect immediately and let the coil and battery cool. Inspect for a shorted winding, damaged enamel, bare wire touching the core, an unintended permanent connection or incorrect battery voltage. Replace damaged wire and shorten subsequent tests. Do not resume with a battery that is swollen, leaking or visibly damaged.
Compass reading is confusing
Move the permanent magnet, steel tools, speakers, motors and other magnetic objects farther away. Energize the coil only while taking the reading and allow the compass needle time to settle.
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A small spark can result from inductive kickback as the coil’s magnetic field collapses. Use a switch or insulated connector, keep fingers away from the break, and check that the battery is not being shorted. Stop if sparking is substantial or accompanied by unusual heat.
Why the coil can spark or heat
Current in the coil stores energy in its magnetic field. When the circuit is opened, that field collapses and can induce a brief voltage across the opening connection—inductive kickback. This is why disconnection can spark even though the circuit used a low-voltage battery. The coil also heats when current flows through its resistance; a short, long test, high current or damaged insulation can increase heating. The referenced lab discusses the voltage surge, but a transient shock should not be described as categorically harmless. See the kickback discussion in the Concepts in Electricity lesson.
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