SOLENOID
Solenoid (from the Greek "solen" - "tube" and "eidos" - "kind") is a cylindrical bobbin, which consists of a large number of conducter loops, wound close to each other. While electric current passes through a solenoid, inside and outside of the solenoid magnetic field appears. Intensity of the field is proportional to the current intensity and (approximately) to the number of the loops. Solenoid with a magnetic core costitutes an electromagnet.