electro-magnet

from The Century Dictionary.

• noun A magnet which owes its magnetic properties to the inductive action of an electric current.
• noun If an insulated wire is wound about a bar of soft iron and a current of electricity is passed through it, the bar becomes a temporary magnet with a north and a south pole; the end at which the current circulates through the wire in the direction of the hands of a clock, as the observer looks at it, is the south pole. In practice, an electromagnet has ordinarily a horseshoe form. It consists of two cylinders, or cores, of soft iron, fastened together at one end and each wound many times with insulated wire; the wire must be so wound that if the horseshoe were straightened the direction of winding would be the same throughout. An electromagnet may be made very powerful, so as to support a ton or more. The soft iron core retains its maximum magnetization only so long as the current is passing, and loses nearly all of it the instant the current ceases. This principle is made use of in the telegraph (which see), electric clocks, electric callbells, etc. If the core is made of steel, it becomes under the action of the current a permanent magnet.

from the GNU version of the Collaborative International Dictionary of English.

• noun A mass, usually of soft iron, but sometimes of some other magnetic metal, as nickel or cobalt, rendered temporarily magnetic by being placed within a coil of wire through which a current of electricity is passing. The metal is generally in the form of a bar, either straight, or bent into the shape of a horseshoe.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a temporary magnet made by coiling wire around an iron core; when current flows in the coil the iron becomes a magnet