Basic Electrical Theory
METHODS OF PRODUCING VOLTAGE (ELECTRICITY)
Example:
Have you ever walked across a carpet and received a shock when you touched a
metal door knob? Your shoe soles built up a charge by rubbing on the carpet, and
this charge was transferred to your body. Your body became positively charged
and, when you touched the zero-charged door knob, electrons were transferred to
your body until both you and the door knob had equal charges.
Magnetic Induction
A generator is a machine that converts mechanical energy into electrical energy by using the
principle of magnetic induction. Magnetic induction is used to produce a voltage by rotating
coils of wire through a stationary magnetic field, as shown in Figure 13, or by rotating a
magnetic 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 will
be studied in more detail in the next two chapters "Magnetism," and "Magnetic Circuits."
Figure 13 Generator - Electromagnetic Induction
Piezoelectric Effect
By 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. Electrons
leave one side of the material and accumulate on the other side, building up positive and negative
charges on opposite sides, as shown in Figure 14. When the pressure is released, the electrons
return to their orbits. Some materials will react to bending pressure, while others will respond
to twisting pressure. This generation of voltage is known as the piezoelectric effect. If external
wires are connected while pressure and voltage are present, electrons will flow and current will
be produced. If the pressure is held constant, the current will flow until the potential difference
is equalized.
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