(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

In the circuit in the figure below, the reading of the ammeter is the same when both switches are open and when both switches are closed. What is the unknown resistance R? (Let R1 = 103 Ω, R2 = 279 Ω, and R3 = 46.0 Ω.)

2. Relevant equations

Adding Resistance in Series: R1 + R2 = Req

Adding Resistance in Parallel: 1/R1 + 1/R2 = 1/Req

V = IR ... I = V/R

3. The attempt at a solution

I believe you have to find the resistance in both cases, switch open and closed, and then set them equal because I = V/R is equal in both cases, so R must be equal, since V doesn't change (always 1.5).

For switch OPEN, I got: Req,open = R2 + R1 + R3

For switch CLOSED, I got: Req, closed = R2 + (1/R1 + 1/Runknown)^-1

I set these equal and solved for Ruknown and got 316.8, but that isn't right. Any tips? Thank you!!!

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# Homework Help: Finding an Unknown Resistance of circuit

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