Uses of Electromagnets
A type of magnets, electromagnets, are usually pieces of a conductor that offer high conductivity, that demonstrate magnetic properties when an electric current is applied. Electromagnets generally consist of a wire wound tightly over a core made from ferromagnetic or ferromagnetic materials. When an electric current is passed through the wire, a magnetic field is created as a result of the electric field. This magnetic field is concentrated on the core of the electromagnet. The electromagnet functions as a magnet only as long as constant electric currents are given to it; that is, the magnetic field is dissipated when the supply of electric current is stopped. Electromagnets have an advantage over ordinary magnets in that the amount (degree) of magnetism offered by the electromagnet can be altered by changing the electric current offered to it. The higher the electric current supplied, the higher is the magnetic property demonstrated by the electromagnet. However, unlike normal magnets, they require an electric current to operate.
Ferromagnetism is the essential phenomenon responsible for the formation of magnets and the reason behind other materials being attracted by a magnet. Among the different kinds of magnetism discussed in physics, ferromagnetism is the strongest type and is also the most commonly found magnetism, like in the case of household magnets. Ferromagnetism is often confused with ferrimagnetism, which is the magnetic property of some materials that have opposing magnetic moments, otherwise known as antiferromagnetism. Permanent magnets and all the materials attracted to a magnet are either ferromagnetic or ferrimagnetic in nature. The common ferromagnetic materials are iron, cobalt, nickel and most of their alloys, and some compounds of rare earth metals. Ferromagnetic materials can be classified into two types as follows.
- Soft ferromagnetic materials: These magnetic materials do not stay magnetized after being subjected to a magnetic field. E.g., Annealed iron.
- Hard ferromagnetic materials: Opposite to soft ferromagnetic materials, these will always act as a magnet once magnetized. E.g., Alnico.
Uses of Electromagnets
Based on their usage, there are two types of electromagnets. Portative electromagnets are only meant to hold an object in place. Tractive electromagnets offer a force and help in moving an object. Owing to their convenient features, electromagnets are used in various instruments and fields. Some are discussed below.
- Electric motors and generators: Motors are electric instruments that convert electrical energy into mechanical energy. Electric motors generally consist of a magnet/electromagnet, a shaft, rotor, bearing etc. among other components. When an electric current is supplied to the motor, the electric current passes through the wire windings of the electromagnet and thereby magnetizes the core. The electric field created, in turn, induces a magnetic field that acts on the shaft. This shaft starts rotating due to the magnetic field and produces rotational movement and torque. Generators have a similar working principle to a motor, but in the case of generators, mechanical energy is converted to electrical energy.
- Electric bell and buzzers: When an electric current is applied to the bell and buzzers, the electromagnetic coils are magnetized by the induced magnetic field. This makes a spring-loaded arm magnetically attracted to the electromagnet. At the end of the metallic arm, a spherical ball is connected, which comes in contact with the gong. When the arm moves to strike the gong, it breaks the circuit, and the arm comes back to its original position and completes the circuit, which then magnetizes the arm to strike the gong again. This process is repeated as long as the bell is rung. A buzzer uses the same working principle, but it is significantly quieter because it does not use a gong.
- Loudspeakers and headphones: Speakers and headphones primarily work by converting electric energy to mechanical energy. They have a diaphragm that can be moved by the audio signals accordingly. When an electric current is given, the electromagnets in loudspeakers and other audio devices, in general, are magnetized. When an input of an audio signal is received by the speaker, the electronics in it amplify the audio signals considerably, enabling the speaker driver to read it. In accordance with the input audio signals, the speaker driver can move the diaphragm to reproduce the sound corresponding to the original unamplified electronic audio signals.
- MRI scanners: The human body is made of tissues that contain hydrogen nuclei, which houses a single proton. Since protons are affected by external magnetic fields, they can produce minute but measurable signals. These generated signals can then be measured in terms of the density of that tissue in one particular area. MRI scanners, therefore, create strong magnetic fields, which are then targeted on the part of the body of the patient that is to be scanned.