It’s a familiar race against time. Your phone is beeping, telling you its battery is almost flat. Meanwhile, you’re hunting through tangled cables for the right one. The simple solution would be to do away with power cables and utilise wireless charging. This is the idea behind an emerging technology with roots in a principle known as electromagnetic induction.
If you send an electrical current through a conductive coil, it produces a magnetic field. You can do this by wrapping wire around a nail and connect each end to a battery. The nail becomes magnetic.
The process can also be reversed. Pop a magnet in a wire coil and it will generate a brief electric current. This happens because the magnet pushes and pulls electrons, which are negatively charged, in the metal wire.
This type of energy production underlies the principle of electromagnetic induction, first outlined by English physicist Michael Faraday in 1831.
So how does this relate to wireless charging?
Let’s use our rapidly dying mobile phone battery and a charging pad as an example.
The pad contains a wire coil which is hooked up to a power supply (in this case, the mains power).
Electrons flow through the wire to generate an electromagnetic field. But because mains power is alternating current – that is, it flips back and forth many times a second – the resulting magnetic field also periodically reverses.
When you place your phone atop this switching magnetic field, the electrons in a coil inside the phone will also be tugged backwards and forwards.
This movement is converted into direct current which charges the battery. Voila! Crisis averted.
Jake Port contributes to the Cosmos explainer series.