When an electric current passes through the coil in an electromagnet, the coil generates a magnetic field. This magnetic field can attract or repel magnetic objects around it, thus realizing functions such as movement between objects, force transfer and energy conversion. Unlike permanent magnets, the size and direction of an electromagnet's magnetic field can be precisely adjusted according to the size and direction of the current.
Electromagnets are widely used in various fields, such as electronics, mechanical engineering, medical equipment, transportation and so on. For example, solenoid locks, maglev trains, solenoid valves, magnetrons, etc. are common examples of solenoid applications. In addition, electromagnets can also be used as an important tool for studying electromagnetic phenomena in the laboratory.
In short, the solenoid is a device that can control the size and direction of the magnetic field, which has a wide range of applications, and is an indispensable component of modern engineering and technology.