Kirchoff's current law for an opamp

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Homework Help Overview

The discussion revolves around applying Kirchhoff's Current Law (KCL) to an operational amplifier (op-amp) circuit. Participants are tasked with identifying a boundary around the op-amp and analyzing the currents at the junctions where the wires connect.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the appropriate boundary to draw around the op-amp and the implications of KCL. Questions arise regarding the validity of current equations based on the circuit configuration and the significance of current magnitudes.

Discussion Status

Some participants have offered interpretations of KCL and its application to the op-amp, while others express confusion about the exercise's purpose. There is an ongoing exploration of the implications of current magnitudes and their significance in the context of the op-amp's operation.

Contextual Notes

Participants are navigating the challenge of understanding the exercise's requirements and the assumptions related to ideal op-amp behavior, such as negligible input currents.

-EquinoX-
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Homework Statement



http://img3.imageshack.us/img3/3939/opamp.jpg

Draw an imaginary boundary around the op-amp, and apply KCL at the five wires that intersect the boundary

Homework Equations





The Attempt at a Solution



I am having quite a problem understanding the question above... which boundary should I draw around? Could someone point this out?
 
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You draw a closed line around the op-amp that contains only the opamp and a part of the 5 wires that connect to it. According to KCL the sum of all the currents going into the opamp
must be 0.

This is an extremely unhelpful exercise, if the goal is understanding op-amps.
 
so is it:
i2 + i3 + i7 -i4 - i6 = 0

is this true?

based on the number that is there?
 
-EquinoX- said:
so is it:
i2 + i3 + i7 -i4 - i6 = 0

is this true?

based on the number that is there?

Yes. Of course, with an ideal op-amp I2 and i3 will be 0.
 
Now what does it mean when the question asks:

Discuss the significance of the relative current magnitudes??

what kind of answer should I provide?
 
I2 will be very small, and I3 will be very small .
which of the other currents would YOU like to be small?
Tell where you think most of the current comes from, and where most of it goes to .
 

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