Fundamentals of Magnetism Automotive Service Technician

Figure 1 - Iron filings placed over a permanent magnet. Magnetic fields are a naturally occurring phenomenon

Figure 2 - Horseshoe and bar magnets. Magnetism exists in a constant form known as a permanent magnet.

It also exists as an induced/electro magnetic field.

Figure 3 - Operation of a compass. Magnetic fields are oriented by using the terms North and South to identify the lines of flux.

Figure 4 - Magnet and magnetic flux lines. Lines of flux exit in a pattern surrounding a magnetized substance or permanent magnet itself. These principals are commonly seen our modern day navigation systems which are oriented by the poles of the earth: North and South.

Figure 5 - Flux lines showing direction, parallelism and not crossing. Magnetic Lines of flux are a force field produced around a magnetic object with a polarity of N to S travel in constant attraction to one and other.

Figure 6 - Magnets attracting (unlike poles attract) Unlike poles attract, Like poles repel

Figure 7 - Unlike poles attract and pull the magnets together.

Figure 8 - Like poles repel (magnets are forced apart).

Figure 9 - Iron has high permeability. Magnetic Fields (Lines of flux) can be manipulated with substances that have high permeability – substances usually containing Iron.

Figure 10 - Plastic has low permeability.

Figure 11 - Attraction of a permeable material to a bar magnet.

Figure 12 - Devices with iron cores. Permeable cores are used to increase the concentration of magnetic fields needed to operate/generate electrical signals or electricity itself.

Figure 13 - Magnetic flux lines cannot be insulated.

Figure 14 - Non-magnetized and magnetized material.

Figure 15 - Current flow in linear and cross-sectional views of conductors.

Figure 16 - Magnetic flux lines surrounding a conductor. Remember that a byproduct of current is magnetism. Every current carrying conductor produces magnetic lines of flux.

Figure 17 - Right-hand rule for conductors. To demonstrate the effect of current flowing in a conductor, we use the “Right Hand Rule” which mirrors the direction of electron flow pointing with the thumb, followed by the lines of flux surrounding the conductor shown by fingers wrapping around the conductor.

Figure 18 - Current in same direction - attract.

Figure 19 - Parallel conductors.

Figure 20 - Current in opposite directions; conductors repel.

Figure 21 - Parallel twisted conductors. (Courtesy General Motors of Canada Limited)

Figure 22 - Conductor formed into a coil to make an electromagnet. By using the magnetic field produced by a current carrying wire, magnetism can be transmitted to a permeable object, therefore making it a magnet.

Figure 23 - Polarity of an electromagnet.

Figure 25 - Right-hand rule for coils.

Figure 26 - Increasing current increases magnetic strength. Simply by increasing the current within a wire we can increase magnetic strength.

Figure 27 - Increasing the number of turns increases the magnetic strength. Additionally, increasing the number of coils of wire increases magnetic strength.

Figure 28 - Moving a magnetic field through a conductor induces a voltage. Not only does current produce magnetism but a magnetic field can produce current. This is called induction.

Figure 29 - Changing the direction of movement of the magnetic field causes a change in polarity of the induced voltage.

Figure 30 - When the conductor moves but does not cross flux lines, no voltage is induced in the conductor.

Figure 31 - A small voltage is induced in the conductor when the conductor moves through the magnetic field at an angle.

Figure 32 - The most voltage is induced in the conductor when it crosses the magnetic field at a right angle. To induce current into a wire, it must be passed through a magnetic field. To induce an adequate current, the wire must cross the lines of flux at a 90 degree angle.

Induction Three factors affecting Induction Speed of wire or permeable object Number of coils of wire Angle which the conductor cuts the lines of flux

Figure 33 - Prior to current starting, there is no magnetic field. A Simple Electromagnet wind a coil of wire around a permeable object

Figure 34 - Flux lines at the instant the switch is closed. apply current to the wire

Figure 35 - Flux lines combine and continue to rise after the switch is closed.

Figure 36 - The magnetic field becomes stationary. increases in concentration until it reaches its saturation limit

Figure 37 - When the switch is opened, the magnetic field starts to collapse.

Figure 38 - The magnetic field collapses rapidly. When the current is removed the magnetic field quick collapses.

Figure 39 - The magnetic field is completely collapsed and high voltage is developed.

Figure 53 - Solenoid in off position To produce work with an electromagnet, a solenoid is a perfect example A coli of wire is wrapped around a moveable permeable object under spring tension

Figure 54 - Solenoid activated. When current is applied, the magnetic field attracts the permeability This mechanical movement can be used to activate switches or valves or locks.

Figure 50 - Relay.

Figure 51 - Relay and circuit with the relay inactive.

Figure 52 - Relay and circuit with the relay activated.

Figure 55 - Field frame with magnets and electric motor armature.

Figure 56 - Electric motor operation. The electromagnetic fields produced by windings of wire attract and repel to rotate a permeable object to make it spin, such as a starter motor.

Figure 57 - Generator and magnetic distributor pickup coil.

Figure 58 - Generation of electrical energy.

Figure 59 -Components of a basic generator.

Figure 60 - Voltage is produced as the rotor turns.

Figure 61 - Rotor turning but no voltage is produced.

Figure 62 - Rotor turning and voltage is produced.