More turns, more pull

A straight wire cannot lift a paper clip. Wire wound round and round, with an iron nail inside, can. A cell must be joined to the wire.

The rule

Wind a wire round and round to make a coil. A rod inside it is the core.

Three things make a coil stronger. More current, an iron core, and more turns at the same current. Cells joined in a row give more current.

Each loop of wire round the core is one turn. Each turn adds its own magnetic field. Iron inside the coil also becomes a magnet.