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Jim McCorison
Posts: **359**

I've warned some of you that while I'm a grizzled old coder, I am somewhat of a novice at the hardware side of things. I am now trying to "fill in the blanks". As such I am starting at the basics and trying to better understand what I've simply excepted as fact before. One thing I've been reviewing is basic analog circuitry. Really basic. Like resistor circuits.

The resistance through a pair of paralleled resistors is defined as (R1 * R2) / (R1 + R2). If R1 is 1K and R2 is 2K, the circuit resistance is 666.67 ohms. Why do you have a resistance that is less than either of the resistors?

Jim

The resistance through a pair of paralleled resistors is defined as (R1 * R2) / (R1 + R2). If R1 is 1K and R2 is 2K, the circuit resistance is 666.67 ohms. Why do you have a resistance that is less than either of the resistors?

Jim

## Comments

747bugg

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So many projects, so little time.

6,491For parallel resistors you can use this formula with any number:

R = 1 / (1/R1 + 1/R2 ... 1/Rn)

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Jon Williams

Applications Engineer, Parallax

Dallas, TX· USA

6,351Haha seems Jon and I were writing the same answer at the same time.

359So to paraphrase, each individual branch allows a certain amount of current to flow. When you add together the current flowing through each resister, the end amount is greater than what the lowest resistance would have allowed, thus the effective resistance of the circuit is less.

Thanks guys,

Jim