Electricity: Magnetic and Heating Effects
Making an electromagnet
Make your own magnet using a nail, a wire and a cell.
If current makes a magnetic field, can we use current to make a magnet?
Try it (Activity 4.2). Take about 50 cm of flexible insulated wire, an iron nail, a cell and some iron paper clips. Wind the wire tightly round the nail as a coil, tape it, and join the ends of the wire to the cell. Bring the nail near the clips: they cling to its ends. Disconnect the wire and the clips drop. Don't keep the wire connected for more than a few seconds, or the cell will run down quickly.
Look closer (Activity 4.3). Roll chart paper into a tube about as thick as a pencil and wind about 50 turns of insulated wire round it: a coil. Put a compass near each end.
| Set-up | What the compasses do |
|---|---|
| coil, no current | nothing |
| coil with current | needles turn: the coil acts like a magnet |
| coil with current and an iron nail inside | needles turn much more, and the nail picks up paper clips |
| current switched off | needles go back: the magnetism is gone |
A coil carrying current that behaves like a magnet is called an electromagnet (electro + magnet). It is a magnet only while the current flows.
Most real electromagnets have an iron core inside the coil, because it makes them much stronger.
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