KinexiaLEARN PHYSICS

Build an Electromagnet

A magnet you can switch on and off with a wire: build one, then make it stronger turn by turn.

Safety:

Disconnect the battery when not testing — the wire can get warm. Never use a wall outlet or high-voltage source; batteries only.

Materials

  • A large iron nail (10 cm or longer)
  • About 1 to 2 meters of insulated copper wire
  • A D-cell battery (or two)
  • Tape
  • Paperclips (20 or more)
  • Sandpaper or a knife (to strip wire ends)

Procedure

1

Wind the coil

Strip about 2 cm of insulation from both wire ends. Starting near the nail head, wind the wire tightly around the nail in neat rows, leaving the two ends free.

2

Power it and count paperclips

Tape one stripped end to the battery's positive terminal and the other to the negative. Touch the nail tip to a pile of paperclips and count how many it lifts.

3

Vary the number of turns

Unwind to half the turns, retest, and record. Then wind double the turns and test again. Plot pickup count against turns.

4

Add a second battery

Add a second battery in series (positive to negative) and count again. Compare with the single-battery result.

5

Test the switch-off and the core

Disconnect one wire while the nail holds clips. Watch them fall — then try a steel nail versus an aluminum or plastic rod as the core.

What to observe

  • Barely any pickup with few turns; many turns lift a chain of paperclips.

  • Two batteries lift noticeably more than one.

  • The nail drops everything the instant you disconnect the battery.

Why it happens

Moving charges create magnetic fields (Ampère's law), and coiling the wire stacks each loop's field in the same direction. The iron nail concentrates that field hundreds of times over, so a modest current lifts real weight. Field strength grows with turns times current (B∝NIB \propto NI) — which is why your magnet gets stronger with more wraps and with a second battery, exactly like the electromagnets in scrapyard cranes and MRI machines.

Try variations

  • Try winding two separate coils on the same nail and powering both — does it beat one long coil?

  • See if your electromagnet can pick up coins. Why do some coins work and others not?