The related structure of the solenoid
(also called the coil coil)
A cylindrical coil uniformly wound by wires, whose length is much larger than its diameter. A magnetic field is generated by a direct current through a wire, and a plug type core is sucked into a solenoid. The motion of a plug type core is often used for driving switches, relays, or other devices.
The magnetic size of the solenoid and the number of coil turns, the thickness of the wire tube, the core of the iron core, the thickness of the core, the coils' density, the core material, are related to the size of the current, the coil material, the size of the voltage.
The relationship between the polarity of the electric solenoid and the direction of the current can be determined by the Ampere rule: holding the solenoid with the right hand and letting the four finger point to the direction of the current in the solenoid, then the end of the thumb is the N pole of the solenoid.