Kirchhoff’s Laws
Kirchhoff’s laws are two mathematical rules used in electrical circuit analysis. The first,
known as
Kirchhoff’s Voltage Law
(KVL) states that the
sum
of the voltages around any
loop in an electric circuit must be zero. Basically, this means that when you get back
around through the voltage differences in the loop to the point where you started, the
voltage there should be what it was before because it can’t have two different values at
the same time. KVL follows from the fact that a good conductor must have zero electric
field inside it. The voltage, then, must be a constant throughout a wire, so working
around the loop to the far end can’t result in a different voltage than the near end.
The normal procedure for applying KVL will be shown in more detail in a subsequent
discussion, but it basically involves following the flow of current around a loop and, as
each circuit element is encountered, writing down a voltage term in a growing equation
that will be set equal to zero at the end. Using Ohm’s law, the voltage across resistors is
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 Spring '11
 Tibbets
 Electrical resistance, Electrical impedance, Voltage drop

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