Re: total resistance in parallel circuits
- From: "Tom Biasi" <tombiasi@xxxxxxxxxxxxxxxxxxx>
- Date: Wed, 5 Oct 2005 18:04:20 -0400
"Midnight Oil" <jamie@xxxxxxxxxxx> wrote in message
news:20051005155041.W32789@xxxxxxxxxxxxxxxxxxxx
>
>
> I am new to electronics, and I've been learning the basics of ohm's
> law. I ran into the formula for finding the total resistance in a parallel
> circuit, struggled with it's meaning...and I want to be sure I understand
> the formula:
>
>
> R(tot) = 1
> -------------
> 1 + 1 + 1
> -- -- --
> R1 R2 R3
>
>
>
> I broke the formula down like this:
>
>
> R(tot) = 1 <--- E (volts)
> ---------------
> 1 + 1 + 1
> -- -- -- <--- I (amps)
> R1 R2 R3
>
>
>
> In other words, the addition of 1/R1, 1/R2, and 1/R3 reveals the
> current when 1 volt is applied to the circuit (E/R). Then, once we know
> the current, we can divide the 1 volt by the current to reveal the total
> resistance R= (E/I).
>
> In other words, 1/Rx reveals the amount of current in one branch of the
> parallel circuit, and adding these together gives us the total current in
> the circuit when 1 volt is applied. If we divide 1 volt by that value, we
> get the resistance in the circuit when one volt is applied.
>
>
> Is my understanding of the equation correct?
>
>
> I thought it was, until I read further in the book. It explained that
> the reason for the 1/Rx was because it is expressing conductivity rather
> than resistance.
>
>
> I thought it was interesting that 2 interpretations of the formula
> could co-exist...or was my own interpretation of the formula wrong?
>
> Is it just a coincidence that the amount of conductance is equal to the
> amount of current flowing when 1 volt is applied?
>
>
> Thanks!
>
> - Jamie
>
>
>
>
>
>
>
> The Moon is Waxing Crescent (7% of Full)
Yes Jamie,
It can be confusing.
If you can use your algebra ( a must in this field) you may better
understand the concept if you consider only two resistances in parallel.
With manipulation you will arrive at the - product over sum - formula. R1 x
R2/(R1 + R2) You can do two resistors (resistances), come to a conclusion,
use the result to combine the other one in the pair.
Then you will appreciate the - one over, one over formula. Yes they are
conductance's. As for you coincidence: is 2+2 the same as 2 squared? Is 4+4
the same as 4 squared?
Review the algebra.
Best Regards,
Tom
.
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