By Chris Deziel, Updated Mar 24, 2022
Discover how electricity and magnetism intertwine by constructing a basic electromagnet. This hands‑on experiment lets you compare the magnetic field produced by a current‑carrying coil with that of a permanent magnet, underscoring the unity of electromagnetic phenomena. The guide stresses safety: use a resistor to limit current and prevent overheating, and always disconnect the circuit when finished.
Wrap a length of insulated 22‑gauge copper wire tightly around a 6‑inch iron bolt or nail. Aim for as many turns as the core allows—too thin a wire risks overheating, too thick limits the number of turns.
Strip the wire ends with a knife and secure one end to the positive terminal of a D‑cell battery using electrical tape. Place a scatter of iron filings on a table, lay the bolt over them, and touch the other wire end to the battery’s negative terminal. Observe the filings forming a pattern, then remove the connection to avoid overheating.
Hold a bar magnet a short distance from the bolt so there is no attraction or repulsion, then touch the wire to the battery terminal again. Notice how the magnet reacts.
Attach a 30‑ohm resistor in series with the coil: connect the free wire end to the resistor and the other side of the resistor to the battery. This limits current, prevents heat buildup, and allows the electromagnet to remain powered safely.
Place the powered electromagnet over the filings, record the resulting pattern, then replace it with the bar magnet and compare. The patterns should be nearly identical, confirming that both are electromagnetic fields. Slight differences reflect the relative strengths of each source.
Position the bar magnet close to the electromagnet to feel attraction. Rotate the magnet 180° so its poles oppose and feel repulsion. This demonstrates that both fields possess distinct north and south poles.
Swap the 30‑ohm resistor for a 100‑ohm one to noticeably weaken the interaction between the magnet and the electromagnet. Reducing coil turns or using a cardboard tube as core also diminishes the field strength.
Always disconnect the wires from the battery when your experiments are complete. Even at low voltage, avoid touching exposed terminals or bare wire ends while the circuit is live. If you detect smoke, unplug the battery and allow the wires to cool before resuming.
