Electromagnetism is one of the fundamental forces of the universe, responsible for everything from electric and magnetic fields to light. Originally, scientists believed that magnetism and electricity were separate forces. But by the late 19th century, this view changed, as research demonstrated conclusively that positive and negative electrical charges were governed by one force (i.e. magnetism).
Since that time, scientists have sought to test and measure electromagnetic fields, and to recreate them. Towards this end, they created electromagnets, a device that uses electrical current to induce a magnetic field. And since their initial invention as a scientific instrument, electromagnets have gone on to become a regular feature of electronic devices and industrial processes.
Electromagnets are distinguished from permanent magnets in that they only display a magnetic attraction to other metallic objects when a current is passed through them. This presents numerous advantages, in that the power of its magnetic attraction can be controlled, and turned on and off at will. It is for this reason that they are used extensively in research and industry, wherever magnetic interactions are called for.
The 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.
By the 1930s, American scientist Joseph Henry made a series of improvements on the design of the electromagnet. By using insulated wire, he was able to place thousands of turns of wire on a single core. As a result, one of his electromagnets could support as much as 936 kg (2,063 lbs) of weight. This was to have a popularizing effect on the use of electromagnets.
An electric current flowing in a wire creates a magnetic field around the wire, due to Ampere’s law. This law states that, for any closed loop path, the sum of the length elements times the magnetic field in the direction of the length element is equal to the permeability times the electric current enclosed in the loop.
To concentrate the magnetic field in an electromagnet, the wire is wound into a coil many times, ensuring that the turns wire are side by side along the edge. The magnetic field generated by the turns of wire passes through the center of the coil, creating a strong magnetic field there. The side of the magnet that the field lines emerge from is defined to be the north pole.
A coil of wire that takes the shape of a helix is called a “solenoid”. However, much stronger magnetic fields can be produced if a ferromagnetic material (i.e. iron) is placed inside the coil. This is what is called a “ferromagnetic-core” (or “iron-core electromagnet”), which can be generate a magnetic field a thousand times the strength of a coil alone.
Then is what is known as a “toirodal core”, in which wire is coiled around a ferromagnetic core takes the form of a closed loop (aka. magnetic circuit). In this case, the magnetic fields take the form of a closed loop, thus presenting much less “resistance” to the magnetic field than air. As a result, a stronger field can be obtained if most of the magnetic field’s path is within the core.
And then there are “superconducting” electromagnets, which are composed of coiled wire made from superconducting materials (such as niobium-titanium or magnesium diboride). These wires are also kept at cryogenic temperatures to ensure that electrical resistance is minimal. Such electromagnets can conduct much larger currents than ordinary wire, creating the strongest magnetic fields of any electromagnet, while also being cheaper to operate because of there being no energy loss.
Today, there are countless applications for electromagnets, ranging from large-scale industrial machinery, to small-scale electronic components. In addition, electromagnets are used extensively for the sake of conducting scientific research and experiments, especially where superconductivity and rapid acceleration is called for.
In the case of electromagnetic solenoids, they are used wherever a uniform (i.e. controlled) magnetic field is needed. The same holds true for iron-core electromagnet, where an iron or other ferromagnetic core can be inserted or removed to intensify the magnet’s field strength. As a result, solenoid magnets are to be commonly found in electronic paintball markers, pinball machines, dot matrix printers and fuel injectors, where magnetism is applied and controlled to ensure the controlled movement of specific components.
Given their ability to generate very powerful magnetic fields, low resistance, and high efficiency, superconducting electromagnets are often found in scientific and medical equipment. These include Magnetic Resonance Imaging (MRI) machines in hospitals, and scientific instruments like Nuclear Magnetic Resonance (NMR) spectrometers, mass spectrometers, and also particle accelerators.
Electromagnets are also used extensively when it comes to musical equipment. These include loudspeakers, earphones, electric bells, and magnetic recording and data storage equipment – such as tape recorders. The multimedia and entertainment industry relies on electromagnets to create devices and components, such as VCRs, and hard disks.
Electrical actuators, which are motors responsible for converting electrical energy into mechanical torque, also rely on electromagnets. Electromagnetic induction is also the means through which power transformers function, which are responsible for increasing or decreasing the voltages of alternating current along power lines.
Induction heating, which is used for cooking, manufacturing, and medical treatment, also relied on electromagnets, which convert electrical current into heat energy. Electromagnets are also used for industrial applications, such as magnetic lifters that use magnetic attraction to lift heavy objects or magnetic separators that are responsible for sorting ferromagnetic metals from scrap metal.
And last, but certainly not least, there is the application of maglev trains. In addition to using electromagnetic force to allow a train to levitate above a track, superconducting electromagnets are also responsible for accelerating the trains to high-speeds.
In short, the uses for electromagnets are virtually limitless, powering everything from consumer devices and heavy equipment to mass-transit. In the future, they may also be responsible for space travel, where ion propulsion systems use magnetic fields to accelerate charged particles (i.e. ions) and achieve thrust.
We have written many interesting articles about electromagnets here at Universe Today. Here’s Who Discovered Electricity?, What Are Magnets Made Of?, How Do Magnets Work?, Earth’s Magnetic Field, and Ion Propulsion.
For more information, be sure to check out NASA Educational Resources’ Experimenting with Electromagnets and Earth’s Role as an Electromagnet and the Creation of Auroras, and NASA Wavelength’s page on Electromagnets.
How Stuff Works also has a great page, titled “Introduction to How Electromagnets Work“, and The National High Magnetic Field laboratory (MagLab) has some wonderful articles on electromagnets, how to make them, and how they work.
You can also check out Astronomy Cast. Episode 103 is about electromagnetic forces.
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