Ohm's Law
In the mid 1800's German physicist, Georg Simon Ohm noticed the following:
There is a direct relationship between the amount of electromotive force applied to a circuit and the
amount of current in the circuit. In other words, if the EMF in a circuit increases by 10%, the current
in the circuit will also increase by 10%.
There is also a direct inverse relationship between the amount of resistance in a circuit and the
current in a circuit. In other words, if the resistance in a circuit increases by 10%, the current in the
circuit will decrease by 10%.
He formulated a mathematical equation to represent these relationships. The equation is known as Ohm's
law.
E = I x R.
This equation can be manipulated with algebra to produce two other formulas:
I = E/R
R = E/I
If you will recall from Chapter One, "E" represents Electromotive force (EMF), "I" represents Current, and
"R" represents resistance. In typical automotive diagnostics, most of Ohm's law calculations are not very
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 Winter '12
 JohnKelly
 Electromotive Force, Magnetic Field, ohm, Georg Simon Ohm

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