Re: electrical power

[Rick Tarara <rtarara@SAINTMARYS.EDU>]

----- Original Message -----
From: "John S. Denker" <jsd@MONMOUTH.COM>

> Justin Parke wrote:
> > Does anyone have any notes written
> > about the distinction between P=VI and P=I^2R?
>
> In an ohmic situation, there is no distinction.
>
> In a non-ohmic situation, P=VI is exact and
> I2^R has no physical significance.
>
> > I understand that the latter refers to
> > "joule heating loss" but I don't feel clear as to why.
>
> P=IV is the Joule heating.
>
> Anything else is an approximation at best.

I guess I don't understand the last part here.  A specific example:  I want
to supply a small town with electrical power.  I need to supply
approximately 10 MW.  I could try and do that at 100,000 V and 100 A, or at
100 V and 100,000 A.  In both cases P = IV = 10MW.  However, for whatever
the resistance of the wires delivering the power, I^2R will be quite
different.

Rick

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Richard W. Tarara
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Saint Mary's College
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rtarara@saintmarys.edu

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