Electromagnets

Activities to try

1. 1

   Electromagnet test bench: isolate what changes the strength

   Why it works: Current produces the coil’s magnetic field, which can be controlled by switching or changing the current. A soft-iron core strengthens the field and usually retains little magnetisation after switch-off. Strength depends on current, turns and core material; changing one measured variable at a time helps isolate a cause.

   1. Build the electromagnet: wind insulated wire around a soft-iron nail and connect it to cells so it picks up paperclips.
   2. Before switching off, predict out loud what will happen to the dangling paperclips the instant the circuit is broken, and WHY.
   3. Switch the current off and observe how many paperclips fall or remain. The current-produced coil field disappears; a suitable soft-iron core usually loses most induced magnetism, but residual core magnetism or sticking can leave some clips attached.
   4. For the current test, keep turns and core fixed and use teacher-approved current-limited settings. Measure the current and record paperclips lifted at each setting, with repeat readings.
   5. For the turns test, keep the core fixed, add turns to the same coil, and check the measured current stays fixed using the approved controls; otherwise note current as a confounding change. Record repeat strength measurements.
2. 2

   Build the idea: single wire → coil → cored coil, and real uses

   Why it works: Magnetism can be CREATED by a current; coiling concentrates it and a soft-iron core strengthens it, and the defining advantage over a permanent magnet is being switchable and adjustable. A magnetic field (from current) is distinct from the electric field around a static charge.

   1. Hold plotting compasses around a single straight current-carrying wire and observe the circular field around it. Compare with a charged balloon: a static charge produces no steady magnetic field. A strongly charged balloon can still tug the needle slightly by electrostatic attraction, but it does not make the steady circular pattern around the wire that the current does.
   2. Coil the wire and observe how the loops' fields add to make a bar-magnet-like field (a solenoid).
   3. Add a soft-iron core and observe the field strengthen.
   4. Match real devices to magnetism CREATED and CONTROLLED by an electric current — scrapyard crane, relay, MRI, maglev — explaining the control each relies on: the crane and relay most clearly switch the magnet on and off, while MRI and maglev depend on strong, current-controlled fields that can be set or varied.
   5. Explain in your own words why a scrapyard crane can pick up AND drop a car just by switching the current, while a simple permanent magnet cannot be switched off to release it.
3. 3

   Diagnose causes and vocabulary: why did the clips fall?

   Why it works: The current produces the coil field; turns are loops of insulated wire on one coil. A soft-iron core is a useful strengthening material with low retained magnetisation, but the core-free coil still produces a field and may lift clips if sufficiently strong.

   1. Answer a diagnostic question on why the paperclips fall off when the current stops, choosing between faulty-cause explanations ('magnetism returns to the power pack', 'the wire overheated', 'the clips repel') and the correct 'no current = no current-produced coil field (a soft-iron core keeps only a little residual magnetism)'.
   2. Sort proposed changes into those that DO and DON'T increase strength (e.g. more current, more turns, soft-iron core vs copper core); and address 'voltage-only' reasoning by noting that strength is set by the current through the coil (adding cells raises both voltage and current together).
   3. Fill in the key vocabulary: turns, insulated, soft iron.
   4. Predict whether a coil with current but NO iron core would still deflect a compass, and whether the nail stays magnetic after disconnection, then justify each answer.