Op Amp Vout Calculation for Non-Inverting Configuration

[esob]

Homework Statement

Solve for Vout

Homework Equations

Vout=Vin(1+Rf/R)

The Attempt at a Solution

I get it is a non-inverting op amp but there is no resistor from the non-inverting terminal to the output.
I have no idea how the equation would be. I understand that noninverting is Vout=Vin(1+Rf/R) but this op amp doesn't match that form and I have never solved one like this.

 

[DaveE]

Have you covered the ideal op-amp approximations in your class yet? I would start with those and then write the equations that relate the node voltages via the amplifier function and the feedback relationship from the output to the inverting input, etc.
If the equations and the algebra aren't clear to you you could try guessing at some numbers and then evaluating what that implies for the other node voltages. For example, what if the input was 2V and the output was 4V, would the amplifier equation be satisfied? If not what adjustments would you make to make everything agree? Then what would that mean for the equations relating those node voltages?

 

[DaveE]

BTW, you didn't say, but I'm assuming that this is a voltage amplifier.
Also, you should probably double-check that you have drawn your schematic correctly. There is something minor about your circuit that is uncommon in real world applications.

 

[gneill]

Hi esob,

Consider that there is feedback to the negative input of the op-amp via the parallel connection of C and R_f
(whatever that net impedance happens to be). There's negative feedback so that will drive the two op-amp inputs to the same potential. That's just the way (ideal) op-amps behave. Doesn't matter what the form of the feedback is; If it's there, it''ll get the job done and drive those inputs to the same value.

What can you say about the potential at the V⁺ input?

I'm not sure how much more to give away here without seeing some of your own work to get a feeling for your level of understanding of the material, so I'd like to hear (okay, see) your thoughts so far.

 

[LvW]

Esob - are you familiar with the interdependences between time and frequency domain?
Do you that a capacitor constitures something like a resistance for sinusoidal signals (called "impedance")?
Do you know the expression for such an impedance ?
Do you know how to combine an impedance with an ohmic resistor?