Kirchhoff and Potentials question.

In summary: These two currents must be equal, so you can write this as an equation: \frac{V_a - V_b}{6k} = -\frac{V_a - V_b}{6k}, which simplifies to V_a - V_b = V_b - V_a = 0. This is just one equation, you need to write one for each node and then solve the system of equations.In summary, the conversation discusses a homework assignment on a circuit problem involving Kirchhoff's laws. The student is seeking help from others on the assignment and is trying to understand how to apply the laws to solve the problem. They also mention a mistake in the problem and request clarification on certain terms. The summary advises writing equations
  • #1
Soliduz
3
0
Excuse me but, this is a rough translaton from a Portuguese homework.
Also, excuse me for my lack of knowledge in some physics, I do a programming course and one of the teachers said we had to know about this.

Homework Statement


http://img181.imageshack.us/img181/7084/87202322av0.jpg [Broken]
http://g.imageshack.us/g.php?h=181&i=87202322av0.jpg [Broken]Taking into account the circuit above, answer these questions:
a) What is the value of i1, i2, i3
b) Calculate the potentials Va, Vb, Vc, Vd, Ve and Vo taking in account the ground (sorry I don't know the correct term, it's the value on the right.

Homework Equations


Kirchhoff law i1 = i2 + i3
V = RI
U = V - RI

The Attempt at a Solution


This teacher is known for being nasty with the students and he gave us this homework without any explanation only saying that we'd need to know about the Kirchhoff laws.
I only found about you guys today, and this homework is due tomorrow (it's worth the grades for the bimester)
So if possible, help! I'm reading a lot of books ATM and will keep updating here 'til the time to deliver the work.

Thanks in advance.
 
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  • #2
Hmm, I'd wager that fish don't get thirsty at all.

Anyway, as you said you have to use KCL and KVL. Write a loop KVL equation for I1, I2, I3 around the left circular mesh and one for the right mesh, plus KCL. Then solve for the unknowns.

As for the potentials, note that you didn't specify which point in the circuit it taken to be ground reference; your picture shows the ground node in the middle of the wires and not connected to them.
 
  • #3
That'About the ground reference, that's how it is on paper.
There is a third question that asks what would happen if it changed to Vo.

Btw Co is should've been Vo. Sorry for the mistake.
 
  • #4
Well, assuming Co is the ground potential, then you should use some nodal analysis to get the currents. Forget about KVL for now and the mesh analysis earlier, write a node current equation for every node Va, Vb, Vc, Ve. Note that by KCL, current flowing into a node = current flowing out of it.
 
  • #5
Sorry, but what does KVL and KCL mean? I think I'm lost in translation here.
I got the part that in = out. I'm having problems finding out which equation I should use for the nodes. Should I do something like U = V ± R . I ?
If so, how should I put it from Va to Vb and from Vb to Vc ? U = V ± R . I1 + I2 + I3 ?
Thanks for the help!
I know very little physics though and since school ended (quite long ago) I haven't looked into it much.
 
  • #6
KVL = Kirchoff's voltage law
KCL = Kirchoff's current law

You need to write an equation for the current flowing out and into each and every node. For example, the current flowing from Va to Vb across the 6k resistor is given by [tex]\frac{V_a - V_b}{6k}[/tex]; current from Vb to Va in the opposite direction along the same path is given by [tex]-\frac{V_a - V_b}{6k}[/tex].
 

1. What is Kirchhoff's voltage law?

Kirchhoff's voltage law states that the sum of all the voltage drops around a closed loop in a circuit must equal the sum of all the voltage sources in that loop.

2. What is Kirchhoff's current law?

Kirchhoff's current law states that the total current entering a junction in a circuit must equal the total current leaving that junction.

3. How do Kirchhoff's laws apply to circuit analysis?

Kirchhoff's laws are used to analyze electrical circuits by applying them to a closed loop or junction in the circuit, and setting up equations based on the voltage drops and current flows.

4. What are potentials in Kirchhoff's laws?

Potentials refer to the voltage values at different points in a circuit. In Kirchhoff's laws, they are used to determine the voltage drops and sources in a circuit.

5. How are Kirchhoff's laws used in real-world applications?

Kirchhoff's laws are used in a variety of real-world applications, including designing and analyzing electrical circuits, troubleshooting electrical problems, and developing electrical systems for various industries such as telecommunications, automotive, and aerospace.

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