Hard intro circuit problem! help please! im stuck on this one for hrs!

1. Feb 28, 2013

nchin

http://imageshack.us/photo/my-images/585/circuitzzz.png/

i thought maybe i should ignore everything that is on the right side of the 3v and just focus on the left side. but this one is not looking too good for me.

any ideas on this one??

2. Mar 1, 2013

Simon Bridge

Re: Hard intro circuit problem! help please! im stuck on this one for

It looks like it should respond to mesh analysis.
What's the problem?

One way to sort your head out about this sort of problem is to redraw the circuit in a way that makes more sense to you. Since there is an explicit ground in this diagram, it may help to draw a ground rail across the bottom of the page and draw the other components in above that ... i.e. the ground rail has three resistors connected to it...

3. Mar 1, 2013

nchin

Re: Hard intro circuit problem! help please! im stuck on this one for

find volt across the 2mA source

4. Mar 1, 2013

nchin

Re: Hard intro circuit problem! help please! im stuck on this one for

how many mesh loops do we have here??

5. Mar 1, 2013

ehild

Re: Hard intro circuit problem! help please! im stuck on this one for

Yes, it is a good idea. See picture.

ehild

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6. Mar 1, 2013

Simon Bridge

Re: Hard intro circuit problem! help please! im stuck on this one for

A fair few - but you don't need all of them.

7. Mar 1, 2013

nchin

Re: Hard intro circuit problem! help please! im stuck on this one for

I1 = V/R
I1 = 3/3+3+2+3+2

8. Mar 1, 2013

nchin

Re: Hard intro circuit problem! help please! im stuck on this one for

i found i1 = 0.6409 A
i2 = 0.2307
total Resistance = 13.588Ω

so i1 - i2 x total R = volt across the 2mA?

is that correct

9. Mar 1, 2013

ehild

Re: Hard intro circuit problem! help please! im stuck on this one for

No.
Only resistors in series add up. There is I2 current flowing through the left 2kΩ resistor. It is not in series with the other ones.

ehild

10. Mar 1, 2013

nchin

Re: Hard intro circuit problem! help please! im stuck on this one for

i see, so what do i do? im not sure how to solve I1, i think i did I2 correctly though

11. Mar 1, 2013

nchin

Re: Hard intro circuit problem! help please! im stuck on this one for

i think i got it, since one of the nodes are grounded out

I1 = 3/6+5 = 0.2727A right?

12. Mar 1, 2013

ehild

Re: Hard intro circuit problem! help please! im stuck on this one for

Write KVL for the loop in the figure, and substitute I2 = I1+2

ehild

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13. Mar 1, 2013

nchin

Re: Hard intro circuit problem! help please! im stuck on this one for

applying KVL = 6I1 - 3 +5I1 + 2I2= 0?

Last edited: Mar 1, 2013
14. Mar 1, 2013

ehild

Re: Hard intro circuit problem! help please! im stuck on this one for

yes.

ehild

15. Mar 1, 2013

nchin

Re: Hard intro circuit problem! help please! im stuck on this one for

it should be .002 right? because 2 mA = .002 A. after i got the currents, what would the total resistor be to plug in the equation V = i x R?

16. Mar 1, 2013

nchin

Re: Hard intro circuit problem! help please! im stuck on this one for

Also I got I1 = -0.2727A and I2 = 1.727A
do i add them together to get the the current i need to solve the problem?

1.727 + (-.2727)?

17. Mar 1, 2013

ehild

Re: Hard intro circuit problem! help please! im stuck on this one for

You substituted the resistance in kΩ-s, then the currents must be in mA.

What should be 0.002?

ehild

18. Mar 1, 2013

nchin

Re: Hard intro circuit problem! help please! im stuck on this one for

oh i see. i thought it was KVL = 6I1 - 3 +5I1 + .002I2= 0

19. Mar 1, 2013

nchin

Re: Hard intro circuit problem! help please! im stuck on this one for

im not sure what im suppose to do after i got the currents though

20. Mar 1, 2013

ehild

Re: Hard intro circuit problem! help please! im stuck on this one for

You multiply the current with the resistance to get voltage.
Have you got the currents? What are they?

ehild