An electromagnet is a magnet that runs on electricity. Unlike a permanent magnet, the strength of an electromagnet can easily be changed by changing the amount of electric current that flows through it. The poles of an electromagnet can even be reversed by reversing the flow of electricity.
An electromagnet works because an electric current produces a magnetic field. The magnetic field produced by an electric current forms circles around the electric current, as shown in the diagram below
If a wire carrying an electric current is formed into a series of loops, the magnetic field can be concentrated within the loops. The magnetic field can be strengthened even more by wrapping the wire around a core. The atoms of certain materials, such as iron, nickel and cobalt, each behave like tiny magnets. Normally, the atoms in something like a lump of iron point in random directions and the individual magnetic fields tend to cancel each other out. However, the magnetic field produced by the wire wrapped around the core can force some of the atoms within the core to point in one direction. All of their little magnetic fields add together, creating a stronger magnetic field.
As the current flowing around the core increases, the number of aligned atoms increases and the stronger the magnetic field becomes. At least, up to a point. Sooner or later, all of the atoms that can be aligned will be aligned. At this point, the magnet is said to be saturated and increasing the electric current flowing around the core no longer affects the magnetization of the core itself.
History of Electromagnets:
he first recorded discovery of the relation between electricity and magnetism occurred in 1820, when Danish scientist Hans Christian Orsted noticed that the needle on his compass pointed away from magnetic north when a nearby battery was turned on. This deflection convinced him that magnetic fields radiate from all sides of a wire carrying an electric current, just as light and heat do.
Shortly thereafter, he published his findings, showing mathematically that an electric current produces a magnetic field as it flows through a wire. Four years later, English scientist William Sturgeon developed the first electromagnet, which consisted of a horseshoe-shaped piece of iron wrapped with copper wire. When current passed through the wire, it would attract other pieces of iron, and when the current was stopped, it lost magnetization.
Though weak by modern standards, Sturgeon’s electromagnet demonstrates their potential usefulness. Despite only weighing 200 grams (7 ounces), it could lift objects that weighed approximately 4 kg (9 pounds) with only the current of a single-cell battery. As a result, research began to intensify into both electromagnets and the nature of electrodynamics.
A portative electromagnet is one designed to just hold material in place; an example is a lifting magnet. A tractive electromagnet applies a force and moves something.
Electromagnets are very widely used in electric and electromechanical devices, including:
- Motors and generators
- Electric bells and buzzers
- Loudspeakers and headphones
- Actuators such as valves
- Magnetic recording and data storage equipment: tape recorders, VCRs, hard disks
- MRI machines
- Scientific equipment such as mass spectrometers
- Particle accelerators
- Magnetic locks
- Magnetic separation equipment, used for separating magnetic from nonmagnetic material, for example separating ferrous metal from other material in scrap.
- Industrial lifting magnets
- magnetic levitation, used in a maglev train or trains
- Induction heating for cooking, manufacturing, and hyperthermia therapy
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