Iron Core Solenoids

An iron core has the effect of multiplying greatly the magnetic field of a solenoidcompared to the air core solenoid on the left.

Electromagnets are usually in the form of iron core solenoids. The ferromagnetic property of the iron core causes the internal magnetic domains of the iron to line up with the smallerdriving magnetic field produced by the current in the solenoid. The effect is the multiplication of the magnetic field by factors of tens to even thousands. The solenoid field relationship is

and k is the relative permeability of the iron, shows the magnifying effect of the iron core.

Induction Motor Actions

Induction motors use shorted wire loops on a rotating armature and obtain theirtorque from currents induced in these loops by the changing magnetic fieldproduced in the stator (stationary) coils.

At the moment illustrated, the current in the stator coil is in the direction shown and increasing. The induced voltage in the coil shown drives current and results in a clockwise torque.
Note that this simplified motor will turn once it is started in motion, but has no starting torque. Various techniques are used to produce some asymmetry in the fields to give the motor a starting torque.

DC Motor Operation

This is an active graphic. Click on bold type for further illustration.

AC Motors

AC Motor

As in the DC motor case, a current is passed through the coil, generating a torque on the coil. Since the current is alternating, the motor will run smoothly only at the frequency of the sine wave. It is called a synchronous motor. More common is theinduction motor, where electric current is inducedin the rotating coils rather than supplied to them directly.

One of the drawbacks of this kind of AC motor is the high current which must flow through the rotating contacts. Sparking and heating at those contacts can waste energy and shorten the lifetime of the motor. In common AC motors the magnetic field is produced by an electromagnet powered by the same AC voltage as the motor coil. The coils which produce the magnetic field are sometimes referred to as the "stator", while the coils and the solid core which rotates is called the "armature". In an AC motor the magnetic field is sinusoidally varying, just as the current in the coil varies.

SIMPLE ELECTRIC MOTORS

This site features award-winning, easy-to-build, and inexpensive electric motors originally designed by Stan Pozmantir for his science fair project in 1997-2000.

If you are looking for a simple science project, or if you wish to learn about electricity, magnetism, and electric motors, this web site has it all! It includes assembly instructions, a section devoted to how these motors work, and here you can find all parts necessary to build these motors.

The brushless DC motors shown on this site are extremely simple, and at the same time very stable, reliable, and efficient. The reed switch motor is the easiest electric motor anyone can build (and understand how it works!).
The motors shown on this page were widely used for educational purposes in different schools and colleges in the United States and other countries. The kits listed here helped the students to learn basics of electricity, magnetism, and electronics. Many people successfully built these motors using simple and clear instructions that were first published in May 1999.