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Assume that the op amp in the circuit shown is ideal.

a.) Find the output voltage when the variable resistor Rx is set to 60k

Assuming Ideal Op amp. All currents leaving nodes are negative.

V+ = V- = 0 and In = Ip = 0

-ip - iRx + iR2, so iR2 = ip + iRx, as ip = 0

iR2 = iRx

-in + iR3 -iR1, iR3 = in + iR1, as in = o

iR3 = iR1

iR2 = Vs/R2 , iRx = Vs/Rx (is Rx in parallel or series?).

iR3 = Vo/R3, iR1 = VR1/R1

so far is this correct? Is Rx in series or in parallel with R2? Im pretty sure its in parallel(as the current has 2 different paths to go.) but im not sure. The V+ = V- = 0 and i+ = i- = 0 assumptions are confusing me at the moment.

Some of the other unknowns can be reduced by voltage dividers. My main problem is determining the Nodal Voltage formulas on these circuits. I had a go anyway.

(Vn-Vo)/R1 + Vo/R3 + (Vs-Vp)/R2 + Vp/Rx = 0

im guessing this is probably wrong. If anyone could give me some pointers in the right direction I would be very grateful. Im going to review Nodal analysis at some point tomorrow and have another go at the problem.

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# Homework Help: Op Amp circuit analysis

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