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Electromagnets

by Ron Kurtus (revised 31 December 2012)

An electromagnet is a type of magnet where its magnetic field is created and controlled by electricity. Electromagnets are made by winding an insulated wire around an iron rod or similar metal core and then passing electric current through the wire. The electric current causes the atoms in the core to align, turning it into a magnet.

The direction of the windings and the current determines which end of the electromagnet is the north (N) pole and which is the south (S) pole of the magnet.

A major feature of an electromagnet is that you can adjust the strength and direction of the field, including turning it on and off. This allows for a number of applications.

Questions you may have include:

This lesson will answer those questions. Useful tool: Units Conversion



What is an electromagnet?

An electromagnet is a magnet that is controlled by electric current. It is made by winding insulated wire around an iron or ferromagnetic core and passing electrical current through the wire.

Note: Ferromagnetic materials are those strongly attracted by a magnetic force.

(See the lesson on Magnetic Materials for more information.)

Also note: If the wire was not insulated, the current would short-circuit through the core. Also, if the wire is too thin, it may get warm from the resistance due to the electricity passing through it.

Simple electromagnet

A simple electromagnet can be made by wrapping an insulated wire around an iron nail and using a battery to provide the electric current.

Creating a simple electromagnet using a nail

Creating a simple electromagnet using a nail

The nail will become magnetized, such that you can use it to pick up paper clips or other small iron objects.

Factors in electromagnet strength

The type of metal in the core, the number of windings, and the amount of current determine the magnetic strength.

If the metal core is a "soft" ferromagnetic material, such as soft iron, the electromagnet loses its magnetism when the electric current is turned off. It becomes magnetized again when the current is turned on.

Changing the direction of the current changes the direction of the magnetic field. If alternating current (AC) electricity is used, the electromagnet has the same properties of a magnet, except that the polarity reverses with the AC cycle.

Note that it is not a good idea to try to make an AC electromagnet. This is because of the high voltage in house current. Using a wire around a nail would result in a blown fuse in the AC circuit box. There is also the potential of an electric shock.

How core becomes magnetized

The way the ferromagnetic core becomes magnetized starts with the fact that electric current passing through a wire creates a magnetic field around the wire. Wrapping the wire in a helix coil concentrates the magnetic field and gives it a N-S direction, as seen in a solenoid.

(See the lesson on Solenoids for more information.)

Direction of atoms become aligned

Atoms in a permanent magnet are aligned such that their magnetic fields create north and south magnetic poles in the magnet. Atoms in a ferromagnetic material—such as an iron rod—can be made to align by wrapping wire around the rod or core and sending electrical current through the wire.

Wrapping the wire around an iron core greatly increases the magnetic field as the atoms line up in N-S (north-south) directions.

Direction of magnetic field

To find the direction the magnetic field is going, you can use the "right-hand rule" to determine it. If you take your right hand and wrap it around the wire, with your thumb pointing in the direction of the electrical current (positive to negative), then your fingers are pointing in the direction of the magnetic field around the wire. Try it with the picture above.

You can also see the direction of the magnetic field by placing a compass near the wire.

Uses of electromagnets

Electromagnets are used in many common devices, such as:

(See the lesson on Electromagnetic Devices for more information.)

Summary

An electromagnet is a type of magnet where its magnetic field is created and controlled by electricity. Electromagnets are made by winding an insulated wire around an iron core and then passing electric current through the wire. The electric current causes the atoms in the core to align, turning it into a magnet.

The direction of the windings and the current determines which end of the electromagnet is the north (N) pole and which is the south (S) pole of the magnet.

A major feature of an electromagnet is that you can adjust the strength and direction of the field, including turning it on and off. This allows for a number of applications.


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Resources and references

Ron Kurtus' Credentials

Websites

Electromagnet - Wikipedia

Electromagnets - HyperPhysics

Magnetism Resources

Books

Top-rated books on Electromagnetism


Questions and comments

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.


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