Time crumbles things; everything grows old under the power of Time and is forgotten through the lapse of Time.

Aristotle, 352 BC

Lord, why is it that wisdom comes so late and life is so short?

Turan Gönen

Today, the phenomenon of magnetism* is used in the operation of a great number of electrical apparatus including generators, motors, transformers, measuring instruments, televisions, radios, telephones, tape recorders, computer memories, computer magnetic tapes, car ignition tapes, refrigerators, air conditioners, heating equipment, and power tools. A material that has the ability to attract iron and steel is called a magnet. Magnets can be categorized as being permanent or temporary, based on their ability to retain magnetism. Figure 3.1a shows a permanent (bar) magnet and its magnetic ™eld. Notice that the magnetic ˆux (Φ) lines (i.e., the magnetic lines of force†) are continuous, and come from the north pole and go toward the south pole. The direction of this ™eld can be established using a compass (which is simply a freely suspended magnetized steel needle) since the marked end‡ of a compass needle always points to the earth’s magnetic north pole. As shown in Figure 3.1b, when a permanent magnet is placed near a metal, the magnetic lines go through the metal and magnetize it. If two permanent magnets are located close together as shown in Figure 3.1c, the magnets are attracted toward each other since the direction of the magnetic lines of force of both magnets is the same. However, if the two magnets are located in the opposite direction as shown in Figure 3.1d, the two magnets are repelled and forced apart since the magnetic lines of force go from north to south and are opposing.