An electromagnet is a type of magnet in which the flow of an electric current produces a magnetic field. If the flow of electric current disappears, the magnetic field and its effect also disappear.
There are different types of electromagnets, and their classification depends on the direction of the current and the desired power.
The solenoid is the most common type, which is a wire coil wound around a metal core. When current passes through the coil, it creates a magnetic field that can be used to attract or repel objects.
Other electromagnets include the horseshoe magnet. It consists of two parallel bars of ferromagnetic material with a coil of wire wrapped around them and the bar magnet. The bar magnet is a permanent magnet with an electrically conductive coating.
How does an electromagnet work?
An electromagnet works thanks to the property that all electrical conductors experience. When a current flows through a conductor, it creates a magnetic field.
The simplest electromagnet is a metal wire wound into a copper wire. A cylindrical coil with a wire wound in a helix shape is often called a solenoid; a closed solenoid would be a torus. The ends of the cable are connected to a power source.
Stronger magnetic fields can be produced if a core of a paramagnetic or ferromagnetic material is placed inside the coil. Usually, a soft iron core is used. The center concentrates the magnetic field so that it will be stronger than if there were only the coil winding. Therefore, the magnetic strength depends on the electrical current flowing through it.
An electromagnet can work with both alternating current and direct current.
The magnetic fields originated by the coils follow the right-hand rule. As a result, if the fingers of the left hand are bent in the current flow direction through the loop, the thumb points in the magnetic force’s direction.
The side of the magnet from which the field lines arise is the North Pole.
Examples of electromagnets
These elements can be used directly or indirectly. In both cases, we can find the following examples:
1. Electric motors
Electric motors use electromagnets to convert electrical energy into mechanical energy. When the current is turned on, it creates a magnetic field that interacts with the magnets in the motor to create rotational force.
2. Electric generators
The operation of an electric generator is based on the principle of electromagnetic induction. The amount of current generated depends on the strength of the magnetic field, the speed at which the conductor is moving, and the size of the conductor.
These engines are used in various applications, including power plants, automobiles, and portable electronic devices. For example, power plants use electric generators to convert mechanical energy from steam turbines into electrical energy that can be transmitted over power lines to homes and businesses. Likewise, automobiles use electric generators to convert mechanical energy from the engine into electrical energy that can be used to power the lights, radio, and other accessories. Finally, portable electronic devices such as cell phones and laptop computers often use small electric generators to charge their batteries.
3. Electric locks
One typical example of an electromagnet is an electric lock. When a button is pressed to open a door, electricity flows through a coil of wire inside the lock. This creates a magnetic field that activates a solenoid, which opens the door.
4. Electromagnetic brakes
When the current is turned on, the electromagnetic brake creates a strong magnetic field that resists the motion of a rotating shaft. This resistance causes the shaft to slow down or stop. Electromagnetic brakes are used in a variety of applications, such as automotive brakes and parking brakes.
5. Maglev trains
Maglev trains use electromagnets to levitate above the tracks on which they travel. The magnets create a magnetic field that interacts with the earth's magnetic field, causing electromagnetic forces to float the train.
This system allows maglev trains to reach very high speeds, as there is no friction between the train and the track.
6. Magnetic resonance imaging (MRI)
Magnetic resonance imaging is a machine that uses strong magnetic fields to generate images of the inside of the human body. Giant electromagnets located outside the machine produce these magnetic fields.
7. Memory storage devices
Memory storage devices such as computers and credit cards also use this technology. The data on these devices is stored in the form of tiny magnetic particles on a spinning disk or strip of tape.
When the device is turned on, an electromagnet reads the data from the disk or magnetic tape and converts it into electrical signals that can be processed by the computer. In the same way, disk and tape recorders use the same technic.
8. Communication devices
Many communication devices use electromagnets. For example, the microphone in a telephone converts sound waves into electrical signals that are sent along a wire to the speaker at the other end of the call.
Similarly, the antennae in radios and televisions receive electromagnetic waves from broadcasting stations and convert them into electrical signals that can be amplified and sent to speakers.
9. Automatic doors
Automatic doors use this technology to keep a door closed, ensuring its opening during a power outage.
Around 1980, the magnetic field derived from an electromagnet began to be used in construction and, more precisely, in security windows.
A Swiss company began to produce an electromagnet, of very small size and weight, which, when supplied at low voltage (12Vdc - 24 Vdc), developed a magnetic field capable of withstanding a force of several thousand newtons.
This application was a great success in emergency exits because it guarantees security against theft without needing to use mechanical parts. At the same time, it ensured the door's opening, without human intervention, in case of power failure.
The evolution of this system has led the construction sector to massively use the electromagnet as an electrical closing element. Today it is used in various ways depending on the dimensions, uses, profiles and type of door.
Other examples
-
To deflect electrically charged particles, as in cathode ray tubes, or particle accelerators.
-
To lift large masses of iron. Some cranes use powerful industrial electromagnet to hook and lift scrap iron.
-
Closure of electrical contacts on relays or operating valves on solenoid valves.
-
To magnetically separate metals in recycling centers.
Who Invented the Electromagnet?
The inventor of the electromagnet was the English physicist William Sturgeon in 1825.
The first electromagnet was a horseshoe-shaped piece of iron surrounded by a coil. In this horseshoe, when the current passed through the coil of the electromagnet, it became magnetized, and when it stopped, it was demagnetized.
Sturgeon demonstrated the magnetic properties of the electromagnet by lifting about 4 kg with a piece of iron weighing less than 200 grams with a coil through which the current of a single-cell battery passed.
In addition, Sturgeon could regulate his electromagnet by varying the intensity of the electric current.
What are the differences between a magnet and an electromagnet?
The most important differences between a permanent magnet and an electromagnet are the following:
-
The magnetic field of an electromagnet can be manipulated quickly by controlling the amount of electrical current. On the contrary, it is necessary that there be a continuous supply of electrical energy to maintain the field.
-
The magnetic force of the electromagnet depends on the electrical supply. If the current stops flowing, the electromagnet loses its properties.
