What is an electromagnet?

The word "electromagnet" is composed of two words, ‘electro’ and ‘magnet’. It is a type of magnet in which an electric current helps in the generation of a magnetic field. Electromagnets usually consist of two major parts, wire and a coil around which the wire is wound. This is called a solenoid. When an electric current is allowed to pass through the coiled wire, the electric current produces a magnetic field. This magnetic field is present only when current is passing through the wire.

An electromagnet is a strong magnet. It is composed of a wire wound around an iron core. When electricity passes through the wire, a magnetic field is produced and magnetic north and south poles are created. But this property vanishes once the electric current is stopped. The property of magnetism is exhibited by ferromagnetic materials such as iron, cobalt, nickel, and most of their alloys.

The invention of electromagnets

The invention of the electromagnet is attributed to William Sturgeon in the year 1824. He was an electrical engineer and a former soldier. Sturgeon wound a wire around an iron rod which was in a horseshoe magnet shape, and saw that the iron rod was exhibiting magnetic properties and had strong magnetic strength, even stronger than the permanent magnet.

The formation of electromagnets

Electromagnets are formed by winding a wire around an iron as its core material. A current-carrying wire produces a magnetic field. That magnetic field has magnetic field lines which eventually form north and south poles around the core and hence the core starts acting like a magnet. The core will exhibit magnetic properties only until the current is allowed to pass through the wire. When the current is stopped, there are neither magnetic field lines nor magnetic poles.

An electromagnet can also be created at home in a very few easy steps. For that, we would need an iron nail, a battery, and a copper wire. First, wrap the copper wire around the nail in such a way that there should not be any air gap. Connect the ends of the wire to the positive and negative ends of the battery. Once electric current starts flowing through the wire, there exists a magnetic field around the iron nail. Since the magnetic field lines are invisible, one can check for the magnetism by bringing another iron nail or a steel nail or paperclip closer to the wire wound nail and check whether it gets attracted towards the wire wound nail. We can also check the response of the wire wound nail when the ends of the wire are removed from the battery source. We can easily see that as soon as the current stops flowing through the wire, the nail slowly stops behaving like a magnet.

Force of an electromagnet

When an electrical current is passed through the solenoid, it results in a magnetic field that exerts force on nearby ferromagnetic objects. The magnitude of the force exerted by an electromagnet is calculated with this equation:

$F = \frac{{(n\times i)}^2\times magnetic cons\tan t \times a}{(2\times g^2)}$

Where, F = force in Newtons

i = current flows in amperes

g = length of the gap between the solenoid and a piece of metal

n = number of turns in the solenoid

a = Area of cross-section

The magnetic constant = 4 x pi x 10^-7.

The Lorentz force is the sum of magnetic and electric forces on a charged item.

Properties of an electromagnet

An electromagnet has a few very important properties. They are as follows:

• The most notable property of an electromagnet is that it is temporary.
• It can very easily be demagnetized by just switching off the power supply or stopping the current flow through the wire.
• The north and south poles of an electromagnet can easily be reversed by just reversing the flow of current.
• The magnetic property of an electromagnet is temporary. Though the magnetic property stays for some time after the current flow is stopped, it goes away after some time and the coil starts behaving like a normal ferromagnetic material.
• The magnetic property of an electromagnet is not supported at high temperatures. It stops exhibiting magnetic properties when the temperature rises.
• The strength of the magnet varies directly with the amount of current passing through the coil and number of wire coils.

Electromagnets and magnets

Electromagnets and magnets have a lot in common. Electromagnets are also magnets, but they are not permanent. They are temporary magnets that exhibit magnetic property only when an electric current is passing through the wire wound around the coil in the electromagnet.

Electromagnets also have magnetic north and south poles just like a normal magnet. The only difference is that they lose their polarity when the flow of current stops.

Electromagnets produce very strong magnetic field strength but normal permanent magnets do not exhibit this strong magnetic field strength.

A very important distinction between a magnet and an electromagnet is that in magnets, the polarity can or cannot be reversed depending upon the type of magnet. In the case of the permanent magnet, the polarity cannot be reversed. But in the case of temporary magnets, the polarities can be reversed in certain cases. In the case of electromagnets, the polarities can easily be reversed by reversing the current flow.

Comparing electromagnets and permanent magnets

A comparison between magnets can only be made when we know the purpose. Once the use of the magnet is known, only then we can figure out which one to pick, whether electromagnet or permanent magnet because both have their advantages and disadvantages.

Permanent magnets have fixed polarities but polarities of electromagnets can be changed. Hence when we require the polarity to be changed in a device, we would use an electromagnet. Electromagnets have a strong magnetic strength but they cannot withstand high temperatures. Hence, we can choose either of them based on our requirements.

National High Magnetic Field Laboratory

The National High Magnetic Field Laboratory (MagLab) performs magnetic field research in physics, biology, bioengineering, chemistry, geochemistry, and biochemistry. It is situated at Florida State University, the University of Florida, and Los Alamos National Laboratory in New Mexico. There are twelve such high magnetic facilities in the world. The MagLab holds a world record for possessing the world's strongest magnet for nuclear magnetic resonance spectroscopy experiments.

Usage of electromagnets

• Electromagnets are used in a lot of our day-to-day life. It is used in a lot of our household items such as washing machines, TV, and refrigerators.
• Electromagnets are present in most motors and generators.
• Electromagnets are used in transformers.
• They are present in most of our doorbells and buzzers.
• They are also used in advanced medical equipment such as magnetic resonance imaging (MRI) machines.
• They are also present in our headphones and loudspeakers.
• They are present in protective devices such as relays. Relays are switches that are electrically operated. They are used to open or close a circuit.
• Maglev (or magnetic levitation) is a system of through which trains can trace their roots using two sets of electromagnets.

Context and Applications

This topic is applicable for students who are studying the following courses:

• Bachelors in Technology (Electrical Engineering)
• Masters in Technology (Electrical Engineering)
• Bachelors in Science in Physics
• Masters in Science in Physics

Practice Problems

Q 1. Which of the following is a permanent magnet?

1. Electromagnet
2. Horseshoe magnet
3. iron nails
4. metal paper clips

Answer: b

Explanation: Electromagnets are temporary magnets. The core will act as a strong magnet only until the current is passing through the wire wound across that core. Horseshoe magnets are permanent magnets and they never lose their magnetic property.

Q 2. In which of the following devices do we use electromagnets?

1. Fan
2. Heater
3. Relays
4. Boiler

Answer: c

Explanation: Electromagnets are installed in relays. Relays are switches that are electrically operated. They are used to open or close a circuit.

Q 3. Which of the following material cannot be made a permanent magnet?

1. steel
2. iron
3. soft iron
4. none

Answer: c

Explanation: Soft iron cannot retain magnetic property at high temperatures and hence cannot be a permanent magnet.

Q 4. In which of the following devices are the temporary magnets used ?

1. MRI machines
2. Motor
3. Generator
4. All of the above

Answer: d

Explanation: Temporary magnets are used in MRI machines, motors, generators, and many other devices.

Q 5. Which of the following is the most important criterion for the electromagnetic field to exist? 

1. Decreasing current value
2. Increasing current value
3. Voltage
4. Vacuum

Answer: c

Explanation: Voltage is the most important criterion for an electromagnetic field to exist. The potential difference causes current to flow and as a result, an electromagnetic field is created.

Common mistakes

Do not confuse an electromagnet with a temporary magnet. An electromagnet is a type of temporary magnet. All electromagnets are temporary magnets but not all temporary magnets are electromagnets.

An electromagnet shows magnetic properties only until the current is passing through the wire wound around the coil. It loses its property once the current flow is stopped.

Do not confuse electromagnetism with electromagnetic induction in which a conductor is placed inside a magnetic circuit to produce electric current.

Related concepts

• Permanent magnets
• Temporary magnets
• Motor
• Generator
• Transformers
• Induction effect
• Magnetism
• Electricity
• Ferromagnetism