two resistances (R1, R2) in parallel can be replaced by a single resistance of value
R = R1R2/R2+R2. Is this correct?

 

Double check what you wrote. My guess is that you made a simple typo.

Second, the way you write the equation is ambiguous. Is the denominator just R2, or is it (as you entered) R2+R2? The use of parentheses might be called for here.

 

Double check what you wrote. My guess is that you made a simple typo.

Second, the way you write the equation is ambiguous. Is the denominator just R2, or is it (as you entered) R2+R2? The use of parentheses might be called for here.

oh, did I? Is it not (R1*R2)/(R1+R2)?

 

oh, did I? Is it not (R1*R2)/(R1+R2)?

It is, but that is not what you originally wrote (and why it was suggested as a typo).

You can also use the

form (shown for 3 resistors in parallel, but this can be expanded for any number of parallel resistors).

 

Rather than trying to memorize any formula for resistances in series or parallel all you have to recall is:

For resistances in series, you add resistance.

For resistances in parallel, you add conductance.

...which ought to be intuitive.

 

It is, but that is not what you originally wrote (and why it was suggested as a typo).

You can also use the

form (shown for 3 resistors in parallel, but this can be expanded for any number of parallel resistors).

Thanks. djsfantasi wrote that I had a typo and also missing parenthesis. I wanted to make sure missing "*" was the typo since I assumed that it was self explanatory in the given context.

 

Thanks. djsfantasi wrote that I had a typo and also missing parenthesis. I wanted to make sure missing "*" was the typo since I assumed that it was self explanatory in the given context.

No, your denominator equates to 2*R2... The '*' is typically omitted when the intent is clear.

 

I assume that by now you discovered what I saw as a "typo". In post #3, you wrote the equation correctly and unambiguously. You had repeated R2, (R2+R2), instead of (R1+R2). And the parentheses was necessary to clearly show you intended to divide by the sum.

I'd write out what the original mistaken equation implied, but won't for fear it will only confuse things more. Suffice it to say tat your equation in post #3 is correct.

 

Rather than trying to memorize any formula for resistances in series or parallel all you have to recall is:

For resistances in series, you add resistance.

For resistances in parallel, you add conductance.

...which ought to be intuitive.

Oh, this how the reverse 1/R is called. Nice. +1

 

Yes.

Conductivity = 1/resistivity

Conductance = 1/resistance

 

and remember, for resistances in paralell, the total will alwways be lower than the lowest value.