What is A Magnet

Permanent Magnets

Temporary Magnets



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An electromagnet is a temporary magnet that is magnetized by the magnetic field produced by an electric current in a wire. Electromagnets have magnetic properties only while the current is flowing.

In the simplest form, an electromagnet is a wire that is coiled into one or more coils. This is called a solenoid. Inside this coil is a metal core -- usually an iron alloy. When electricity flows through the wire, a magnetic field is generated. While current flows, the core acts like a magnet. When the current is stopped, the core is demagnetized.


Strength of an Electromagnet

If the wire coils are wrapped around something with no magnetic properties -- such as wood -- it will generate a weak magnetic field. If it is wrapped around a ferromagnetic material such as an iron nail, then the magnetic field can result in several hundred- to thousandfold increase in the strength of the field.

Electromagnet Polarity

In an electromagnet, the magnetic field is proportional to the number of coils in the wire, to the cross-section of each loop, and to the current passing through the wire. The electromagnets polarity depends on the direction of the flow of current. The Right-Hand Rule is typically applied, however, which is a theory developed for electromagnetics by British physicist John Ambrose Fleming in the late 19th century.

The Right-Hand Rule

right hand rule

  1. An electric current passes through a solenoid, resulting in a magnetic field. When you wrap your right hand around the solenoid with your fingers in the direction of the conventional current, your thumb points in the direction of the magnetic north pole.

  2. An electric current passes through a straight wire. Here, the thumb points in the direction of the conventional current (from positive to negative), and the fingers point in the direction of the magnetic lines of flux.

Electromagnetic Uses

Electromagnets are commonly used in particle accelerators, motors, and MRI (magnetic resonance imaging) machines. In general, electromagnets are most useful when the magnet needs to be shut on and off, such as in junkyard cranes and other construction cranes.

junkyard crane

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