1942 - 1947 Chevrolet Shop Manual



	12-3

	Another method of checking the polarity of electro magnets is by using the "right hand rule." To do this, grasp the core with the right hand, with the fingers passing around the core in the same direction as the current. The thumb will indicate the north pole. To reverse the polarity of the electro magnet, merely reverse the direction of the current flow through the magnet windings, as illustrated in Fig. 6. This is another very important rule, since it is used frequently when repairing generators. The strength of electro magnets is governed by a unit named "ampere turn." An ampere turn is	Electricity can be produced by various means, most important of which are: 1. By chemical reaction, as in a battery. 2. By mechanical means, as in the generator of an automobile. In order to have a clear understanding of the electrical circuits, it is necessary to know something of the units of measurements and electrical terms used in dealing with things electrical. Volt is the name given to the unit of electrical pressure that forces the current through the electrical wires or circuits. Ampere is the name given to the unit of the amount of current flow. Ohm is the name given to the unit of resistance or opposition to the current flow. Ohms law is a statement of the relationship of voltage, amperage and resistance of a circuit, "the current value in amperes is always equal to the pressure in volts divided by the resistance in ohms." Amperes=Volts div. by Ohms Ohms=Volts div. by Amperes Volts = Amperes X Ohms ELECTRO MAGNETIC INDUCTION The principle of electro magnetic induction is one of the most important electrical laws. Without this law it would be impossible to have generators, telegraph, telephone, radio or ignition apparatus on automobiles. This law or rule is: "In order to produce a current by electro magnetic induction we must either move a conductor so that it cuts across the lines of force of a magnetic field or move a magnetic field so that the lines of force cut across the conductor." Fig. 7.

	Fig, 6-Method of Reversing Polarity of Electro Magnets one compete turn of wire around a core with one ampere flowing through it, for example: Ampere turns = Turns X Amperes The foregoing is all any service man needs to know about magnets to do service work and make practical electrical repairs. ELECTRICITY There are two kinds of current electricity, alternating and direct. Alternating current is not used in the electrical system of an automobile. Direct current flows through its circuit in one direction from the positive to the negative. This is the only type current used in the electric system of an automobile.

		Fig. 7-Principles of Electro Magnetic Induction To demonstrate this rule, take a horseshoe magnet, the lines of force are flowing from the north pole to the south pole. Now, take a piece of wire and move it up and down through the lines of force. The wire cuts the lines of force and a current is generated in the wire by the principle of electro magnetic induction. In this case we were moving the conductor so that it was cutting across the lines of force of a magnetic field. If we move