When an electric current is passed through a wire wound around a conductor (most often ferrous metals), a magnetic field is generated around that conductor. It behaves and possesses all the properties of a true magnet. When the current stops flowing through the wire, the metal loses its magnetic properties. The opposite is also true, i.e., if a wire is moved through a magnetic field (or the magnetic flux around a wire is varied), it produces an electric current in the wire.
Discovery of Electromagnetism
The discovery of electromagnetism has a fascinating history. While the existence of magnetism and electricity as separate phenomena had been ascertained a long time ago, the discovery of the fact that they are different manifestations of the same force came much later. Many great scientists contributed to unraveling electromagnetism, and it would not be fair to credit only a few of them. The most widely known names associated with it are that of Hans Christian Ørsted, Sir Michael Faraday, and James Clerk Maxwell. Ørsted showed that a current deflects the needle of a magnetic compass. He published his results in a journal, which were recognized as very important. Faraday introduced the concept of the field
to describe electromagnetism, which helped to put it in a mathematical framework. Maxwell, one of the greatest physicists of all time, described electromagnetism mathematically. His four crucial equations, known today as the Maxwell equations
, are the basis of describing electromagnetism in physics. Though the full nature of electromagnetism is not completely understood as yet, we still continue to harness the potential of electromagnets as exemplified by the several uses given below.
All types of electric motors work using the same principle. In all electric motors, a current traveling through a wire is acted upon by a magnetic field at right angles to it. The magnetic field creates a force (called torque) that rotates the coil of wire. This is utilized to generate movement for a number of applications in industries and household appliances.
A generator works in exactly the opposite way to that of an electric motor. A wire loop is rotated between two magnets (representing a stationary magnetic field). This generates an electric current in the wire loop, which can be utilized in many different ways.
Relay switches are used in a lot of equipment. The basic functioning of an electromagnetic relay involves generating a magnetic field in an iron core by the passage of an electric current through a coil of wire wound around it. When an electric current passes through the coil, the magnetic field generated makes or breaks of circuit. This basic mechanism is used in a lot of applications.
Particle accelerators, like the now-famous Large Hadron Collider, increase the energy of a beam of particles and provide it with directionality. Huge magnets, known as dipoles, are employed to change the path of a high-energy stream of particles. Quadrupole magnets are used to converge the particles. These magnets are superconducting electromagnets, allowing for a very strong magnetic field capable of bending the path of particles traveling at a speed close to that of light.
Mass spectrometer is an instrument used in analytical chemistry for a variety of purposes, like elucidating the structure of chemical compounds to pharmacokinetics. It functions by fragmenting molecules into charged particles, and then measuring their mass-to-charge ratios. After a compound is fragmented, the charged species are separated by a mass analyzer
. The separation is achieved by the application of electromagnetic fields on the charged species.
Magnetic Resonance Imaging (MRI)
MRI is a well-known technique useful for imaging soft tissues of the body. The MRI machine has superconducting magnets that create a strong magnetic field around the body of the patient. The superconducting magnets are coils of almost zero resistance metal alloys that conduct electricity very efficiently when supercooled. When electricity flows through the coil, it becomes a powerful magnet. The magnetic field generated is used for imaging tissues of the body.
A transformer is a device used for changing the voltage and frequency of an incoming alternating current (AC). It consists of a core of iron around which a primary coil (carrying current from the AC supply lines) and a secondary coil (which carries the modified alternating current) are wound. The incoming current generates magnetic flux in the core. This flux generates the transformed current that flows through the secondary coil. Transformers are of two types: step-up transformers
and step-down transformers
These contain both a permanent magnet as well as an electromagnet. The electromagnet is in the form of a coil of wire known as a 'voice coil'. When electric current passes through the voice coil, it becomes an electromagnet whose polarity changes with the current that passes through it. The magnetic field of the voice coil interacts with the magnetic field of the permanent magnet. This creates a force that moves the coil. The movement of the coil moves the speaker cone attached to it. This process conveys amplified sound that is received as an electrical signal in the speaker.
Magnetic Levitation Trains
Popularly known as Maglev trains or simply Maglevs, these are high-speed trains that have powerful electromagnets to levitate (lift), guide, and move them. The electromagnets lift the train to a few millimeters above the tracks. This greatly reduces friction, which is one of the main hindrances to achieving speed in any kind of transportation. The movement and speed of the train is also regulated by the electromagnets. These trains have been touted as the future of high-speed transportation. As of now, however, Maglevs are in operation in only a few countries of the world.
A popular application of electromagnets is in security systems. Electromagnetic locks, also known as maglocks, consist of a coil of wire wrapped around a metal core. When electric current passes through the coil, the core becomes an electromagnet. It attracts a metal plate on the same side of the door. This is called an 'armature plate'. This results in 'locking' of the door. Maglocks are available in two types (depending upon mechanism of operation). These are called 'fail safe' and 'fail secure'.
Sorting of Scrap Metals
Electromagnets (as well as permanent magnets) are used to sort ferrous metals from other metals in a junkyard. This process works on the principle that ferrous and some other metals respond to magnetic fields. The drawback of this sorting process is that it cannot distinguish between ferrous metals and nickel. Powerful electromagnets are also used to lift heavy metal objects in a junkyard.
Electromagnetism is one of the four fundamental forces of nature. Perhaps this is the reason why the presence of electromagnets is so pervasive throughout the applied sciences. As mankind continues to study other aspects of this phenomenon, we may witness further technological advances arising out of it.