Digital Sound & Music: Concepts, Applications, & Science, Chapter 4, last updated 6/25/2013
Electricity can be understood through an analogy with the flow of water (borrowed from
(Thompson 2005)). Picture two tanks connected by a pipe. One tank has water in it; the other is
empty. Potential energy is created by the presence of water in the first tank. The water flows
through the pipe from the first tank to the second with some intensity. The pipe has a certain
amount of resistance to the flow of water as a result of its physical properties, like its size. The
potential energy provided by the full tank, reduced somewhat by the resistance of the pipe,
results in the power of the water flowing through the pipe.
By analogy, in an electrical circuit we have two voltages connected by a conductor.
Analogous to the full tank of water, we have a voltage an excess of electrons at one end of
the circuit. Let’s say that at other end of the circuit we have 0 voltage, also called ground or
ground potential. The voltage at the first end of the circuit causes pressure, or potential energy,
as the excess electrons want to move toward ground. This flow of electricity is called the
current. The physical connection between the two halves of the circuit provides resistance to
the flow. The connection might be a copper wire, which offers little resistance and is thus called
a good conductor. On the other hand, something could intentionally be inserted into the circuit
to reduce the current a resistor for example. The power in the circuit is determined by a
combination of the voltage and the resistance.
The relationship among potential energy, intensity, resistance, and power are captured in
Ohm’s law, which states that intensity (or current) is equal to potential energy (or voltage)
divided by resistance:
Equation 4.1 Ohm’s law
Power is defined as intensity multiplied by potential energy.
Equation 4.2 Equation for power
Combining the two equations above, we can represent power as follows:
Equation 4.3 Equation for power in terms of voltage and resistance
Thus, if you know any two of these four values you can get the other two from the equations
Volts, amps, ohms, and watts are convenient units to measure potential energy, current
resistance, and power in that they have the following relationship:
1 V across 1 of resistance will generate 1 A of current and result in 1 W of power
The above discussion speaks of power (W), intensity (I), and potential energy (V) in the
context of electricity. These words can also be used to describe acoustical power and intensity as
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