Homework Help: An omp amplifier example

1. Mar 16, 2012

Saeed.z

i came across an example in my text book as shown :

http://img593.imageshack.us/img593/8444/img1314i.jpg [Broken]

if we used KCL and In = 0 :

In = I_100 + I_25

=> I_25 = -I_100

but as being written in the answer , I_25 = I_100 !

could anyone explain it for me ? thanks

Last edited by a moderator: May 5, 2017
2. Mar 16, 2012

technician

No current flows into or out of the + or - inputs of an ideal op amp.
Hope this helps

3. Mar 16, 2012

sandy.bridge

Wouldn't the technical answer be $i_{25}=-i_{100}$ since the direction in the diagram is opposite to the actual direction? My textbooks take into account the assumed direction, and if the final answer is supposed to be opposite to the assumed direction, you merely place a minus sign in front of it to indicate that it is in the opposite direction to the supposed direction.

4. Mar 16, 2012

technician

Completely agree with Sandy Bridge