Is This Ohm's Law Application Correct for an OP-AMP Circuit?

[CoolDude420]

Homework Statement

Hi,

So I'm just curious whether or not the following statement is correct for the circuit shown. It's part of a bigger problem involving OP-AMPS, the part of the circuit shown is the upper loop connecting from the inverting to the output.

I was just having some doubts in my mind and wanted to confirm whether or not the equation i have written is correct.

Homework Equations

Ohms Law. V = IR.

The Attempt at a Solution

 

[gneill]

For the given component values it looks okay. Presumably the rectangular component is meant to represent a 1 F capacitor?

 

[Quandry]

Homework Statement

Hi,

So I'm just curious whether or not the following statement is correct for the circuit shown. It's part of a bigger problem involving OP-AMPS, the part of the circuit shown is the upper loop connecting from the inverting to the output.

I was just having some doubts in my mind and wanted to confirm whether or not the equation i have written is correct.

View attachment 215789

Homework Equations

Ohms Law. V = IR.

The Attempt at a Solution

View attachment 215790

Interestingly gneill seems to understand your circuit and terminology, but I am struggling with it. However, any way I look at it I can't see the rectangular component as being a capacitor unless the OP AMP in question is a differentiating OP AMP and even then I would need to see a feedback resistor which is a key part of the the various voltage components. Since we are doing V = IR (or in this case I = V/R) I cannot understand this to be differentiating problem, so I would read that the rectangular component is a resistor with a value of 1/S but I am not able to determine what 'S' signifies. Also, if this is an integrating OP AMP, then there must be two resistor, R input and R feedback.
I may be just having a dumb day, bit I would like to see a full circuit, with the components correctly defined before I could comment on the correctness of the value terminology used in the equation.

 

[gneill]

...so I would read that the rectangular component is a resistor with a value of 1/S but I am not able to determine what 'S' signifies.

The 's' is the Laplace domain "frequency" variable/operator (yes, it's both). Reactive components such as inductors and capacitors have impedances in the Laplace domain of the forms:

Inductance L: sL
Capacitance C: 1/(sC)

Laplace transforms are a very handy way to write and solve differential equations using simple algebra.

 

[Quandry]

It is a sad day when you don't learn something new Although vaguely aware of Laplace transformations I have never used them.
For a differentiating OP AMP I would use the formula I_input = C x dV_input/dt

 

[CoolDude420]

For the given component values it looks okay. Presumably the rectangular component is meant to represent a 1 F capacitor?

Yes! That's exactly what it was meant to be. Thank you