Feb 04, 2022 By Team YoungWonks *
What is an electromagnet? We may have come across this term often and it is also well known that electromagnets are used widely in modern technology, including everyday devices and appliances. In this blog post, we shall take a look at what an electromagnet is, how it functions, its varied applications, and advantages and disadvantages.
What is an electromagnet?
An electromagnet is a type of magnet where the magnetic field is produced by an electric current. Electromagnets are made up of wire wound into a coil. A current runs through the coil of wire building a magnetic field that is concentrated in the hole, indicating the center of the coil. The magnetic field thus created can be even stronger if one winds a wire tightly around a powerful iron core, since iron itself is a magnetic material. The magnetic field strength, in turn, is expressed as the vector H and is measured in units of amperes per meter.
Electromagnets exhibit a few properties as shared below:
Electromagnets attract ferromagnetic materials such as iron, nickel and cobalt.
Like poles of electromagnets repel each other while their unlike poles attract each other.
A freely suspended electromagnet always points in the north-south direction.
The key difference between an electromagnet and a permanent magnet is that an electromagnet has a magnetic attraction towards other metallic objects only when a current runs through it. In fact, the strength of the magnetic force can be controlled by controlling the current flow. This makes electromagnets, also known as temporary magnets, particularly useful, often more than permanent magnets.
For instance, electromagnets can be turned on and off at will and as mentioned earlier, the power of the magnetic field can be controlled. This is why they are used for collecting scrap (particularly pieces of iron and steel) in scrapyards.
The fact that electromagnets can be polarized and changed just by reversing the poles’ directions also makes them very useful, especially for building electric generators or motors.
Brief history of electromagnets
Electromagnets work on the principles of the electromagnetic force, a type of physical interaction that takes place between electrically charged particles.
In 1820, Danish scientist Hans Christian Oersted demonstrated that each time the electric current flows through the wire, a nearby compass needle deflects. Four years later, in 1824, British scientist William Sturgeon invented the electromagnet by using a painted horseshoe-shaped iron piece wrapped around by bare copper wire. Sturgeon also showcased the power of the electromagnet by lifting other iron scraps. In 1830, US scientist Joseph Henry made a more sophisticated electromagnet.
How does an electromagnet work?
When the electric current runs through a straight wire, it creates a magnetic current all around it. A magnetic field intensity can be built up by winding the copper wire in a particular direction. Multiple windings of the copper wire will further increase the intensity. Indeed, the strength of the electromagnet is directly proportional to the number of turns in the coil. So the strength of an electromagnet can actually be doubled by doubling the number of turns. That said, winding the wire in the opposite direction will cancel the effect of previous winding. A straight line of one winding direction to another is needed, one that starts from the end of the winding to multiple windings.
Inside the iron material, each atom behaves like a natural magnet and since they are in random orientation, the effect of the tiny magnet is cancelled out. But when the iron is coiled inside the copper wire winding, the entire tiny magnet inside the winding core aligns itself in the direction of the magnetic field, thus the electromagnetic effect is stronger, giving us a powerful electromagnet.
The strength of the magnetic field is also influenced by the magnitude of the current flowing through it to a saturation point (where all atoms/ions in the core are aligned with the magnetic field). As soon as the flow of current through an electromagnet is stopped, the magnetism effect on the core and in the wires is lost.
Electromagnets can be polarized using the right-hand rule. As per this rule, when we grip the ball with the right-hand thumb, the four fingers holding the flow indicate the direction of current and the thumb points to the magnetic north.
Advantages of electromagnets
The main advantage of using an electromagnet instead of a permanent magnet is that one can control the magnetic field of the former. Not only can one easily turn on and off the device’s magnetic field, with many electromagnets, one can also control the strength of the magnetic field.
Electromagnets are also useful in situations where the changing of poles and discontinuation of the magnetic field is mandated. Magnetic separators capitalize on this very property of electromagnets. When magnetized by passing current, large electromagnets attract the iron scraps from the heap of scraps and once the operator has moved the scrap to another place, the current supply is stopped and at this point the scrap is dropped by them.
Other advantages of electromagnets include the fact that they do not cost much and are rather easy to build. Also, they are lightweight and do not damage the test-piece which is a part of the electromagnet.
Limitations of electromagnets
One of the disadvantages of electromagnets is that they take up a lot of energy and heat up very quickly. This heat generation in turn makes them lose a lot of electrical energy.
To use an electromagnet, one needs a power supply that can provide an electrical current. Some electromagnets are plugged into an electrical outlet, and others contain a battery bank. Permanent magnets, meanwhile, don’t need a power source since they are naturally ferromagnetic.
In other words, maintaining a constant magnetic field needs a continuous power supply in case of electromagnets. Sure an electromagnet can store huge amounts of energy in its magnetic field but the energy will start discharging as soon as the electric current is interrupted.
Also, to get a strong magnetic field, a lot of coiled copper wire is needed and this in turn requires a large space. So electromagnets are not ideal for small spaces. There’s also the danger of a short-circuit that can damage the electromagnets and the surroundings, so care must be taken to avoid this.
Uses of electromagnets
Due to their properties, electromagnets are useful in varied industries and electric and electromechanical devices today. The use cases/ applications for electromagnets include:
- Magnetic separation equipment, used for separating magnetic from nonmagnetic material, for example separating ferrous metal from other material in scrap
- Industrial lifting magnets and magnetic levitation used in trains
- Particle accelerators, magnetic separators
- Electric motors and generators
- MRI machines
- Magnetic locks
- Control switches in relays
- Magnetic recording and data storage devices such as tape recorders, VCRs, hard disks
- Electric bells and buzzers
- Amplifiers, loudspeakers and headphones
- Musical instrument pickups
- Actuators such as valves
- Scientific equipment such as mass spectrometers
- Spacecraft propulsion systems
- Induction heating, for cooking, manufacturing, and hyperthermia therapy
*Contributors: Written by Vidya Prabhu; Lead image by: Abhishek Aggarwal