Question

anyone here good with circuit analysis? (finding voltage, current, etc)

Answer 1

You should just post the question...someone here will likely help you with it.

Answer 2

what's the question?

Answer 3

Yes i am very good with circuit analysis, if u post the question i would be glad to help you out.

Answer 4

i know the voltage divider equation is Vn = (Rn/Rt)*Vt ...

but in the circuit linked below, why does v1 = (5/45)*v0 instead of (40/45)*v0 ?
how does one determine which resistor (the 5K or 40K) to use to find v1??

http://imgur.com/CMCcc

Answer 5

In this ideal OpAmp, v2 must equal vI. Now vI = 5/(40 + 5) . VO, using the voltage divider relationship, because vI must be the potential difference over the 5k resistor.

Now you write down VO.

Answer 6

thanks, but why is V1 the potential difference over the 5k resistor rather than the 40k?

Answer 7

Because call the current running through that branch of the circuit I.

Then VO = I(40k + 5k), or I = VO/(45k)

At the bottom of the 5k resistor, we know the voltage potential is zero. Hence the potential at the top of the resistor, v1, is equal to 5k.I.

Hence
v1 = 5k.I
= 5k/45k

Make sense?

Answer 8

**correction: last step, v1 = 5k/45k . VO

Answer 9

so when i use the voltage divider equation, i should always start at wherever the voltage is 0, then go around the series (in this case, clockwise from ground)?

Answer 10

That's one way to make sure you get the right answer. But another here is intuition. Suppose the 5k resistor went to 0 Ohms. Then v1 would be zero. So if it's a question of whether it is
40/45 VO
or
5/45 VO
then it seems clear it must be 5/45 VO

Answer 11

Ah, i see. I had been trying to follow the direction of the current flow arrows before which here would have me going around the series counter-clockwise. Thank you for helping me! :)

Answer 12

sure thing