> From:         Rick Regan[SMTP:drrdr@CHARTER.NET]
> Sent:         Thursday, April 15, 2004 10:13 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [EE]: Why isn't Ohm's Law written I=V/R?

>   Does anyone know why Ohm's law is writtem V=IR (E=IR)
> instead of I=V/R?  Of course I know they're equivalent.
> I just wondered why - if I is the dependent variable and V
> and R are the independent variables - it's basic form
> isn't I=V/R.

The law stated by Simon Ohm was that the voltage drop
across a resistance was linearly related to the current
through the device. At the time this was "discovered",
nonlinear circuit elements were unknown. How the law
is algebraically stated is irrelevant; both of the above
equations are equivalent and therefore they are both
"Ohm's Law". Which one is used depends on one's
personal history.

Now that semiconductor junctions are commonplace,
it is necessary for engineers to admit that Ohm's Law
is not always correct. The cases for which it does hold
true are referred to as "Ohmic", as in "the voltage between
the collector and emitter of a transistor is the sum of the
junction potentials and the ohmic drops in the bonding
wires".

John Power

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