# i need help , i'dont understand Kirchhoff's laws

#### WBahn

Joined Mar 31, 2012
25,068
you helping me a lot , thank you but the last thing i want it , can you solve this circuit by KVL step by step ? please
No, because that won't help you much. You've probably already seen examples worked for you many times, both in class and in the text. How will seeing yet one more example worked for you suddenly make things clear?

In fact, you should have already had numerous homework problems on circuits this simple. How did you manage to do them? Just guessing here, but you got others to show you how to do them and, in doing so, you thought you had learned something when, in reality, you didn't because YOU didn't have to solve them.

Go back to the section of your text where KVL was first introduced and read it. Then make your best attempt at applying that to this circuit and present it here. That way we can see what you are getting correct and where you are going wrong.

#### RBR1317

Joined Nov 13, 2010
512
No. KCL is only useful at junctions where the current can split and go more than one way. In this circuit, there are no junctions that join three or more branches, so KCL is trivially satisfied and doesn't provide any useful information.
The node equation is a direct application of KCL and will certainly provide the answer to the problem. There is a simple 'machine' method for writing node equations, so it is possible to write the node equations for a circuit without even understanding what is happening in the circuit.

For this circuit it is just necessary to identify the nodes and pick one as a reference GND, then write the node equations for the other nodes - in this case node Vth.

In short, KVL & KCL always work, but node equations (KCL) & the 'method' are fairly simple. Yes, I know you are trying to get the TS to actually understand what is happening in the circuit, but failing that the node equation(s) will always provide the answer. Or am I jumping the gun here, and the TS doesn't have a clue what node analysis and mesh analysis are?

#### WBahn

Joined Mar 31, 2012
25,068
Yes, using KCL via node equations works. I was referring to a more fundamental level (back when all you knew was Ohm's Law and you were just being introduced to KCL and KVL but well before you ever heard of mesh and nodal analysis. But, even there, I was being a bit too extreme when I said that KCL gives you no useful information -- it does, but you have to look at the circuit with a bit more detail than students at that level are generally ready for.

#### Fmrx

Joined Jan 28, 2015
28
Wow wow hold your horses ,how can you have an exam next week known you've never studied kirchoffs. Law ?. It's impossible ,I would help you but saying next week is thrown my off the idea sorry