Why do the iron filings have such good dance moves? Thanks to lots of magnets and electromagnets. Magnets are always magnetic. Electromagnets are only magnetic when you pass current through them. You can therefore turn them on and off.
There are lots of little rods on the tray. Those are the magnets. They attract the iron filings and hold them tight.
The electromagnets are located under the tray, and therefore below the magnets. When a song begins to play, a computer controls when which electromagnets switch on. When they switch on, the magnetic field is amplified. This not only attracts more iron filings, the iron filings also stand upright. By switching the electromagnets alternately on and off, the iron filings dance.
You can also choose which electromagnets you switch on. Press the button and put your fingers on the playing field.
Magnet earth
The earth is actually a giant magnet. That’s because, in the core of the earth, there is a swirling hot metal mass that moves continuously, generating a powerful magnetic field. As a result, your compass needle always points north.
Electromagnets for cooking
Nowadays, you can find an induction hob in many kitchens. This kind of hob contains electromagnets. These create a magnetic field that changes direction very quickly. This ensures that (the appropriate) metal pans heat up.