June 02, 2020
Some materials called ferromagnetic materials can be magnetized, using a large magnetic field to align their internal magnetic orientations. Once magnetized, these materials emit a constant magnetic field.
Yet, there is another way of creating a magnetic field. When electric charges move, they actually create themselves a magnetic field. A constant electric current in a wire will generate a constant magnetic field. The equations that rule this phenomenon are called the Biot-Savart equations.
To make the magnetic field stronger, we usually use a coil instead of a single wire. This device is called an electro-magnet. You can generate a magnetic field by switching on this device (for example, connecting it to a current generator), and turn off the magnetic field by turning off the device.
This device is actually using the reverse principle that is used for a current generator. Instead of moving a magnet inside a coil to move electrons, we move electrons to generate a magnetic field.