Electric motors are found in almost every industry. Few people realise, however, that the path to current electric motor technology lies in the knowledge of magnets and electromagnets. The natural magnet was already known in ancient times. It was known to have the property of attracting small iron objects from short distances. The ore from which natural magnets are made, now called magnetite, was found on the island of Magnesia - hence the name of the magnet. Today artificial magnets with similar properties to natural magnets are made from steel. When a magnet is placed in iron filings, you can see that they adhere to it unevenly. They will adhere to it unevenly: at both ends in the greatest amount, while the closer to the centre they are, the less they will adhere to it. The points in which the magnet is attracted the strongest are called poles. 
[001] Not only natural and artificial magnets, but also electromagnets are subject to the laws of attraction and repulsion. They consist of cores made of soft iron around which numerous coils of insulated wire are wound. When an electric current flows through the winding, the cores become magnets. When the current is switched off, the magnetic properties also cease. The attraction and repulsion of the poles of magnets and electromagnets plays a fundamental role in electrical engineering, especially in electric motors. It is therefore worthwhile to get acquainted with this phenomenon in a simple experiment. Having a good understanding of the operation of electromagnets, we can then proceed to consider the principles of electric motor operation. 
[002] An electromagnet placed between the poles of a permanent magnet and rotating on an axis would work just like a motor if it kept changing current directions. Figure [002] displays a steel magnet, which is referred to as a permanent magnet because of its ability to retain magnetic properties. It has a horseshoe shape. Between its poles you can see an electromagnet placed on a shaft, with which it can rotate. When a current is applied to the electromagnet, a north pole will be formed at its upper end and a south pole at its lower end. It is not difficult to imagine what will happen next. The north pole of the magnet will be repelled by the north pole of the permanent magnet and then attracted by the south pole of the permanent magnet. Simultaneously, the south pole of the electromagnet, repelled by the south pole of the permanent magnet, will move upwards and be attracted by the north pole of the permanent magnet. However, if at this point the connections to the battery can be quickly changed, then the north pole at the top of the electromagnet will reappear, while the south pole at the bottom. In this case the electromagnet will continue to rotate. Of course, it is impossible to make such changes manually several dozen times per minute. Therefore, engineers have constructed appropriate mechanisms which can do this. 
[003] A commutator has been added to the previous circuit, which makes the desired changes every half revolution of the electromagnet around the axis. A simple device that automatically changes the direction of current flow is called a commutator or changer. The ends of the electromagnet windings are connected to two semicircular metal sections, which are fixed on the shaft and mutually insulated from each other and from the shaft. These form a commutator. The current from the battery is carried by two metal strips, called brushes, which touch the commutator. 
[004] First rotor position - the N pole of the permanent magnet attracts the S end of the rotor, the S pole of the permanent magnet attracts the N end of the rotor. Figure [004] shows a rotating electromagnet - called the rotor - in a position where the top forms the south pole and is attracted by the top north pole of the permanent magnet. A commutator mounted on the same shaft rotates along with the rotor. Current from the battery flows through the upper brush and the upstream commutator section and after passing through the winding, it flows away through the lower section and the lower brush. When the end of the electromagnet passes the N pole of the permanent magnet, the situation changes. The upper brush is now in contact with the slice that came from the bottom and current is now flowing through it to the winding. The current then flows away with the opposite slice. The direction of current flow changes and the poles of the rotor also change. As a result, the rotor end becomes the north pole and is repelled in the direction of rotation of the rotor by the north pole of the permanent magnet.
[005] Second rotor position. A motor with a two-pole rotor will not move if the magnet and rotor are facing each other. In addition, it runs unevenly because the rotor is pulled by the change in the attractive force. For these reasons at least three-pole motors are used for propulsion. The current flows through the brush 1 and commutator to the rotor poles 2 and 3 and then returns through the commutator and brush 4. If you think about figure R005, you will see that this motor not only starts at each rotor position, but also makes better use of the magnetic forces. Rotors with several dozen poles are used in industry. These motors run very evenly and start at every position. 
[006] Flow of electric current and action of forces in a three pole electric motor. • • •
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