How do wireless chargers work?

What if you want to charge your phone but don't have a cable? You don't have to worry about that with a wireless charger. In short, you place your device on some kind of mat, and the phone can be charged without a cable (provided your phone supports wireless charging, of course).

Magnet and wire

Let's start with a little demonstration. I have here a coil of wire connected to the galvanometer. A powerful magnet is placed inside the red coil.

If the magnet is simply placed in the coil, the galvanometer does nothing. But if I pass the magnet through the coil, the galvanometer needle deflects, meaning an electric current is generated.

The current was generated because I changed the magnetic flux (not a real thing). There are other ways to change magnetic flux. I like to use rain flux as an example.

There are three ways to change the rain flux. First, you can change the amount of rain. If it rains faster, more water will fall on the paper (note: real raindrops are not shaped like this). Second, you can change the Angle between the paper and the raindrop. Third, you can change the size of the paper. This is the rain flux.

We can do the same thing with magnetic fields. We call this magnetic flux. The magnetic flux depends on the strength of the field, the Angle of the field to the area, and the size of the area.

There are three ways to change the rain flux. When you change the magnetic flux, you create an electric field inside the coil. The field then generates an electric current to charge your phone. Remember, the "change" in magnetic flux is the most important. In fact, with a rotating magnet and an electric coil, you can have as much electricity as you want. It is like petrol powering a generator or a nuclear power station (a nuclear reaction turns water into steam, which then drives a turbine).

There is no magnetic flux of a magnet

There are no magnets in wireless chargers. If you place a live wire on a magnetic compass, you can see that this current also produces a magnetic field. First, you can change the amount of rain. If it rains faster, more water will fall on the paper (note: real raindrops are not shaped like this). Second, you can change the Angle between the paper and the raindrop. Third, you can change the size of the paper. This is the rain flux.

We can do the same thing with magnetic fields. We call this magnetic flux. The magnetic flux depends on the strength of the field, the Angle of the field to the area, and the size of the area.

If you use a moving magnet instead of an alternating current wire, you're ready to go. The varying currents in the wires create varying magnetic fields. The changing magnetic field causes a current to flow through the other coil. The more loops produced, the stronger the effect. Here's a simple version of wireless charging:

At the bottom is a large coil. The coil is connected to a household plug. It's the equivalent of a wire with a plug. When you plug the item in the picture into a socket, an electric current runs through the wire. All the outlets in the house produce alternating current.

This means that the current oscillates at a frequency of 60 Hertz, and the changing current creates the changing magnetic field. On top of the larger coil is a small coil (the thing held by the hand in the picture). The small coil is connected to a small light bulb. When a small bulb is near a changing magnetic field, it generates an electric current. The current is strong enough to light a light bulb.

True wireless chargers are smaller, of course, but use the same principles.

One last question. Earlier, I wondered if I could charge my smartwatch by shaking it. Can we charge our smartwatches with wireless chargers? Of course. However, the smartwatch should be placed directly on the charger. Being too far away won't help -- at least the wireless charger above won't be able to charge a smartwatch from a distance.