Page 33 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

Let’s assume that the contents of the tank are magically maintained at a
constant level. The water pressure at the end of a pipe inside the tank depends
on the depth of the pipe with respect to the surface level. The difference in
pressure between the ends of a pipe inside and outside the tank causes water
to flow. The amount of water flowing through a pipe depends on the water
pressure and on the resistance to that pressure determined by the pipe’s cross-
sectional area. A thin pipe with a smaller cross-sectional area will present more
resistance to the water than a thicker pipe with a larger cross-sectional area.
Thus, if both pipes have the same cross-sectional area, bucket 6 will fill faster
than bucket A.
In electronic systems, the flow of electricity is called current measured in
units of amperes or the resistance to electrical flow is simply called
resistance measured in units of and the electrical equivalent to pressure
is called voltage, or electric potential, measured in units of volts.6
The materials used to connect components in electronic circuits are typi-
cally selected to have low resistance values; however, in some cases engineers
make use of special resistive components called resistors. The value of resistance
( R) depends on the resistor’s length, cross-sectional area, and the resistivity of
the material from which it is formed. Resistors come in many shapes and sizes;
a common example could be as shown in Figure 3-3.7*s

3 The term amp is named after the French mathematician and physicist Andre-Marie Ampere, who
formulated one of the basic laws of electromagnetism in 1820.
4 An amp corresponds to approximately 6,250,000,000,000,000,000 electrons per second flowing past
a given point in an electrical circuit (not that the author counted them himself, you understand;
this little nugget of information is courtesy of Microsoft’s multimedia encyclopedia, Encurta).
5 The term ohm is named after the German physicist Georg Simon Ohm, who defined the relation-
ship between voltage, current, and resistance in 1827 (we now call this Ohm’s Law).
6 The term volt is named after the Italian physicist Count Alessandro Giuseppe Antonio Anastastio
Volta, who invented the electric battery in 1800. (Having said this, some people believe that an
ancient copper-lined jar found in an Egyptian pyramid was in fact a primitive battery. . . there
again, some people will believe anything. Who knows for sure?)
7 In addition to the simple resistor shown here, there are also variable resistors (sometimes called
potentiometers), in which a third “center” connection is made via a conducting slider. Changing
the position of the slider (perhaps by turning a knob) alters the relative resistance between the
center connection and the two ends.
8 There are also a variety of sensor resistors, including light-dependent resistors (LDRs) whose value
depends on the amount of light falling on them, heat-dependent resistors called thermistors, and
voltage-dependent resistors called VDRs or varistors.