Basic Electrical Theory METHODS OF PRODUCING VOLTAGE (ELECTRICITY)Example: Have you ever walked across a carpet and received a shock when you touched ametal door knob? Your shoe soles built up a charge by rubbing on the carpet, andthis charge was transferred to your body. Your body became positively chargedand, when you touched the zero-charged door knob, electrons were transferred toyour body until both you and the door knob had equal charges.MagneticInductionA generator is a machine that converts mechanical energy into electrical energy by using theprinciple of magnetic induction. Magnetic induction is used to produce a voltage by rotatingcoils of wire through a stationary magnetic field, as shown in Figure 13, or by rotating amagnetic field through stationary coils of wire. This is one of the most useful and widely-employed applications of producing vast quantities of electric power. Magnetic induction willbe studied in more detail in the next two chapters "Magnetism," and "Magnetic Circuits."Figure 13 Generator - Electromagnetic InductionPiezoelectricEffectBy applying pressure to certain crystals (such as quartz or Rochelle salts) or certain ceramics(like barium titanate), electrons can be driven out of orbit in the direction of the force. Electronsleave one side of the material and accumulate on the other side, building up positive and negativecharges on opposite sides, as shown in Figure 14. When the pressure is released, the electronsreturn to their orbits. Some materials will react to bending pressure, while others will respondto twisting pressure. This generation of voltage is known as the piezoelectric effect. If externalwires are connected while pressure and voltage are present, electrons will flow and current willbe produced. If the pressure is held constant, the current will flow until the potential differenceis equalized.Rev. 0 Page 21 ES-01
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