Question

voltage divider question

in the circuit linked below, why does v1 = (5/45)*v0 instead of (40/45)*v0 ?

http://imgur.com/CMCcc

Answer 1

I can't access to your given link :(

Answer 2

hm...it works for me...
i'll try uploading it to a different site

Answer 3

Yes please.

BTW: if it is a image then you can attach this file here too by clicking on the Attach File button dear.

Answer 4

does this one work for you?

http://tinypic.com/r/wtywx/6

Answer 5

OK . It is fine for me now.

So it is from Alexander book. Right?

Answer 6

yes, it is. you have the same book :)

Answer 7

I have read that book.

So what is your problem?

You are asking for voltage divider rule.

Answer 8

i know that Vn = (Rn/Rt)*Vt

but i don't understand why they've chosen the 5 kΩ resistor instead of the 40 kΩ resistor for Rn...

Answer 9

if you look then you will find 5K is the resistor with V1 voltage. Not 40K

Answer 10

Sorry, I didn't notice your reply. How can you tell the 5K resistor is the one that determines the V1 voltage?

Answer 11

I thought that usually, we should follow the flow of current from + to - (conventional current) and from what i can tell, the current here will start at V0 and flow first through the 40K resistor, then through the 5K resistor. Right?

Answer 12

that's because v1 is the voltage between the non inverting input (+) and ground, i.e. the voltage across 5K resistor

Answer 13

See, the path to the ground is through 40k and the 5k right? so think of this as a loop in which current flows. Now, if you look at node v1, it is indeed directly in contact across the 5k resistor and ground. So, it becomes a series resistor with 40k n ur voltage divider applies.

Answer 14

thank you, that's actually a perfect explanation. much appreciated.