I'm not real good with this circuit stuff and I have a HW due tomorrow I was wondering if someone could help me with or at least explain how to start the problems.

So far we've learned Ohm's Law, Kirchoff's current and voltage law's and resistors in parallel/series along with voltage and current division.

I'm just confused with how to start the problems applying the stuff Ive learned; any help?

I can help if you ask more specific questions
or maybe show your work

This post was edited by saber_x3 on Feb 18 2014 06:25pm

I posted some pic's of circuits with questions, are they not showing up?

It's pretty easy stuff, I learned most of it in Physics 1 or 2, can't remember which, but that was like a year or two ago and for some reason I can't grasp the concept of how to get these going.

ok, so you don't know how to start this stuff
1. add up resistors to reduce circuit
2. determine what is is being asked for, current or voltage
3. kvl for voltages in a loop, kcl for currents out of node
though they both can be used for either current or voltage, it's your choice to pick the more suitable one

Damn that looks hard as fuck

first two, i would do mesh analysis. but the first one will have a super mesh in it so becareful wit that.

for number 3, use KCL (current in = current out) then use the fact that, there is resistors in parallel so voltage across those resistors are equal.

4th one, simplify the circuit and use voltage across resistors are equal.

This post was edited by FamilyGuyViewer on Feb 18 2014 11:27pm

Yeah, I don't know mesh analysis yet though.
The first two are the only ones I have left to go.

Problem 3
I figured out the voltage was the same, 120V, across the 3 in parallel on the third problem, the used a combination on Ohm's Law and the Power given on the third resistor to use p=iv to find the rest of it. So got the third one.

Actually, for this problem (3) I was unsure if the voltage would remain 120 V across the 3 in parallel since the voltage source would also be in parallel with them... is that a correct assumption?

Problem 4
4th one, not sure if I did it right but I simplified the circuit. Used the equation, V1 = (R_eq/R_total)*(Vs)
Vs = 3 V
R_eq = 50 ohm (just the 75 ohm and 150 ohm resistor in parallel)
R_total = 135 ohm (the resistor equivalent of the entire circuit.)
I got a small number though, V1 = 1.11V, so not sure if it's correct.

*Then for V2 I found the initial current by using V=iR from the R_total and 3V initial voltage, I got 0.222A.
Then found the current through the 30 ohm resistor using the current division equation, i_30 = (R_total/R_30)*(i_s)
i_s = initial current = 0.222A
R_total = 135 ohm
R_30 = 30ohm
I got 1A for the current in the 30 ohm resistor and then from there I just used Ohm's Law to for the voltage, V=iR = (1A)(30ohm) = 30V
Not sure if that's the right way but whatever.

Now I just need help on the first two. I'll probably figure them out by myself but if anyone has any help that would be cool.

I really need to solve these just by using Ohm's Law, Kirchoff's current/voltage Law, Series/Parallel, Current/Voltage division.

This post was edited by TheTown on Feb 19 2014 12:23am

The voltage across those 3 parallel resistors are 120v. However if there were resistors outside of that parallel part.. Then it wouldn't be 120v

Hmm the 2nd one. U can do the sum of the voltage in a loop is zero. Forgot the term for this lol. There won't be current in the middle resistor so u can ignore that when u do the sum of voltage in a loop is zero. And u can find Vab from tat

Last one, wat I would do is find the total current coming out of the voltage source by simplifying the circuit then use a combination of KCL and voltage across parallel resistors are equal. There's probably a shorter step but this is wat I would do. Work backwards to work foward lol


This post was edited by FamilyGuyViewer on Feb 19 2014 12:49am

Alright.



It's called Kirchoff's Voltage law I think is what you're talking about.
Alright, thanks for the help man. I'm pretty sure I figured out the 2nd, 3rd and 4th one but the first one I just really have no idea. It's a tough one.

I pretty much used the middle junction and called it junction a and summed the current going into and out of it for a formula, but the weird part is when you do that, you automatically get the value for i_g so not sure that's correct approach. Then I did two loops one the bottom two and solved for V_g but I don't think it's right.