total resistance in parallel circuits



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)
.

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