Solenoids are used in many ways and have different structure and characteristics. We can describe a solenoid as an electromagnet or device that produce some kind of movement (linear or rotary). Simple solenoids are built of magnetic coil that cause, when current is applied, to a steel arm to move from it’s initial position. This kind of solenoid is a linear solenoid, and it converts electric energy into linear movement. The length of this movement is called stroke and the force of the stroke is measured in Newton (N). Different application requires different stroke and power. You can see how does a simple solenoid is working, and can work both ways in the pictures to the right.
Electromagnetic solenoids are used in many applications. You will find them in door locks, water-pressure valves, robotics systems, MRI machines, hard disk drives, speakers, microphones, power plants, and cars. These are just examples.