A certain circuit is composed of two parallel resistors. The total
resistance is 667 ohms. One of the resistors is 1.0k ohms, What is the
other resistor?

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Howdy chatsukz-ga,

To figure out the total resistance of a circuit of resistors in
parallel, one can use the formula of: 1/Rt = 1/R1 + 1/R2 + ...

In your example, we then have: 1/667 = 1/1000 + 1/R2

One way to solve this problem is to first convert 1/667 to a common
denominator of 1000.

If we divide 1000 by 667 we get (rounded) 1.5/1000 for the left side
of the formula: 1.5/1000 = 1/1000 + 1/R2

We can then take 1/1000 from each side, leaving: .5/1000 = 1/R2

Solving for R2 we then get: .5/1000 = 1/2000

So, the other resistor (R2) in the example is 2.0k or 2000 ohms.

If we plug this back into the original formula, we get:

1/Rt = 1/1000 + 1/2000
1/Rt = 1/1000 + .5/1000
/1Rt = 1.5/1000
1/Rt = 1/667 (rounded)
Rt = 667

If you need any clarification, please feel free to ask.


Search strategy: Experience with electronic circuits.

Looking Forward, denco-ga - Google Answers Researcher

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Clarification of Answer by denco-ga on 18 Oct 2005 18:52 PDT

Of course, in my answer:

1/Rt = 1/1000 + 1/2000
1/Rt = 1/1000 + .5/1000
/1Rt = 1.5/1000
1/Rt = 1/667 (rounded)
Rt = 667

Should have read:

1/Rt = 1/1000 + 1/2000
1/Rt = 1/1000 + .5/1000
1/Rt = 1.5/1000
1/Rt = 1/667 (rounded)
Rt = 667

"Rt" is meant to represent "Resistance (total)" as well.

Looking Forward, denco-ga - Google Answers Researcher

Thank you!!! Nice explanation there.

You are welcome, chatsukz-ga, and thanks for nice comment and 5 star rating.

Looking Forward, denco-ga - Google Answers Researcher