4.2 Electromagnets

A single straight wire’s magnetic effect is weak. But coil that wire into many loops and the magnetic effects add up — turning the coil into a real, switchable magnet.

Activities 4.2 & 4.3 — Build an electromagnet Wind insulated wire tightly into a coil (around a paper cylinder or an iron nail) and connect the ends to a cell. Place compasses at the coil’s ends: their needles deflect, showing the coil is now magnetic. Slip an iron nail into the coil and the deflection jumps — and the nail’s ends grab iron paper clips. Disconnect the cell and the magnetism vanishes, dropping the clips. (Connect only for a few seconds at a time, or the cell weakens quickly.)

What Is an Electromagnet? A current-carrying coil that behaves as a magnet is an electromagnet. Adding an iron core (like a nail) inside the coil makes it much stronger, which is why most practical electromagnets have an iron core. Unlike a permanent magnet, an electromagnet is switchable — it is magnetic only while current flows.

An electromagnet has poles, too

Just like a bar magnet, an electromagnet has a North and a South pole (Activity 4.4). You can find them with a compass: since unlike poles attract, if the compass’s north pole is pulled toward one end of the coil, that end is the south pole — and the other end is the opposite.

Making it stronger — or flipping it

Three Controls The strength of an electromagnet can be increased by:

  • using more current (a battery of more cells gives a larger current), and/or
  • winding more turns of wire in the coil, and/or
  • adding an iron core.

And its poles can be reversed simply by reversing the direction of the current. A weak single cell deflects the compass a little and lifts only a few clips; more cells or more turns deflect it more and lift many.

Try it in the explorer below: change the number of cells and turns (with an iron core in place) and watch how many paper clips the electromagnet can hold.

Electromagnet strength explorer
More cells and more turns → stronger field → more clips lifted.
Cells:
Turns:

Science Talk In the explorer, going from 1 cell to 2 cells doubles the lift; going from 25 turns to 50 turns also doubles it. So what happens if you double both at once? Talk through why “more current” and “more turns” both push in the same direction — toward a stronger field.