Amateur Electronics question

[Christian Hofmann]

On Mon, 10 Jul 2000 10:16:08 -0400
"Jon Darby" <jdarby at lplizard.com> wrote:

> Howdy!
>    I officially became fed up of not knowing EXACTLY how all the little
> electronic projects I've built work and deceided to educate myself on
> electronic theory. I have a seriously juvenile resistance question, so I
> figured since everyone on the list must have had a baby-steps phase in their
> education I would ask and not worry too much about being humiliated. Here is
> the formula my book gives for finding total resistance with two resistors
> wired in parallel:
> 
> Rtotal=1/R1 * 1/R2
> 
> Assuming this is the correct formula, shouldn't two resistors with a value
> of 1 each equal a total resistance of 1? The answer the book gave was .5,
> where am I missing the logic? Grrrr! Day two and I'm already stumped. Thanks
> a pantload for any help!

Hi Jon,

The correct formula is 1/Rtotal = 1/R1 + 1/R2
i.e. Rtotal = 1 / (1/R1 + 1/R2)

Taking the value 1 as an example indeed gives 0.5, but not using their
formula... 


As a rule of thumb:

resistors in series 
- add resistance values for total resistance
- resistance increases
                     
resistors in parallel 
- add conductivity values (i.e. 1/R) for total conductivity
- resistance decreases


And for the public humiliation part - we'll leave that for next week.
Be prepared... :-)

regards
Christian

P.S.: after some time of just reading, but not being able to post to the
list, I'm glad to be back. Yippieee...