Can I convert a potentiometer to 2 resistors?

[Femme_physics]

You're right, come to think of it. So no current flows through R1 and R2. My original position was correct in that respect. I'm unfamiliar with the rule that says that if Va and Vb are 4 volts and no current flows through R2 and R1 then Vout must also equal 4 volts...although it does make sense...in this case there's no amplification, though, so the op-amp is kinda useless there

 

[gneill]

You're right, come to think of it. So no current flows through R1 and R2. My original position was correct in that respect. I'm unfamiliar with the rule that says that if Va and Vb are 4 volts and no current flows through R2 and R1 then Vout must also equal 4 volts...although it does make sense...in this case there's no amplification, though, so the op-amp is kinda useless there

It's just the circumstance for one particular setting of the potentiometer. The user can twist the knob to set a desired output, and 4V happens to be one choice. The op-amp is just doing its job to set Vout to a value that makes Va equal to Vb.

 

[Femme_physics]

Fair enough, but just to clarify:

For general cases of an op-amp, when Va = Vb and no current passes through R1 and R2, then Va = Vb = Vout

 

[gneill]

Fair enough, but just to clarify:

For general cases of an op-amp, when Va = Vb and no current passes through R1 and R2, then Va = Vb = Vout

It's certainly true for the given configuration where there's a single input resistance and feedback resistance. Essentially, when there's no current through a resistor the potential must be the same at either end of it. This is true whatever the circumstances. If that resistor happens to be the feedback resistor, then the potentials at the output and the op-amp inputs must be the same.