Finding Voltages Using KVL & KCL

  • Thread starter nothingsus
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In summary, the problem involves determining the currents at different nodes in a circuit with three resistors. The equations used are Kirchhoff's Voltage Law and Kirchhoff's Current Law. The current splits at node A into i_1 and i_2, with i_1 being greater due to the path of least resistance. The direction of i_3 at nodes B and C is unknown and can be assumed either way, with incorrect guesses resulting in negative values. The resistors at the bottom can have different values and will have the same currents i_1 and i_2 if they have the same resistance.
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nothingsus
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Homework Statement


http://imgur.com/a/L82gU
CH27P035.png

[Mod note: Inserted image inline for convenience]

Homework Equations


KVL, KCL

The Attempt at a Solution


[/B]
one of my equations will be at one of the nodes and will include all 3 currents.

i can also draw two loops, one for the upper triangle and one for the bottom triangle, however the signs of the terms will depend on the directions of the current, and I don't know which way i_3 will go!So this is a question from my Physics 2 course.

I've googled online for similar problems however most of them use more advanced techniques like mesh currents which I don't think is expected in my course.

We've only learned
1. algebraic sum of voltages about a closed loop is zero
2. current in = current out at a node

So I'm trying to label which way the current splits and the directions so I can write equations with the two above facts in mind, but I'm not really sure.

current is i_0 between the positive terminal of the battery and node A.

At node A, i_0 splits into i_1 (for the branch with R_1) and i_2 (for the branch with R_2).

i_1 should be greater than i_2 since current takes the path of least resistance.

When i_1 and i_2 reach nodes B and C respectively, I'm not really sure what happens. I don't know what direction (left or right) the current i_3 (flowing through R_3) should be.

Also, since the bottom two resistors are also R_1 and R_2 (although R_1 is now on the left and R_2 is now on the right) would they have the same currents i_1 and i_2 through them? What if they were some other resistances?
 

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  • #2
nothingsus said:
I don't know which way i_3 will go
You don't need to predict it correctly. Just assume one way and write all the equations accordingly. If you guessed wrongly you will get a negative answer.
 

What is KVL and KCL?

KVL (Kirchhoff's Voltage Law) states that the sum of all voltage drops in a closed loop circuit is equal to the sum of all voltage sources. KCL (Kirchhoff's Current Law) states that the sum of all currents entering a node in a circuit is equal to the sum of all currents leaving that node.

Why are KVL and KCL important?

KVL and KCL are important because they are fundamental laws that are used to analyze and solve complex electrical circuits. They allow us to determine unknown voltages and currents in a circuit, making it easier to design and troubleshoot electrical systems.

How do I apply KVL and KCL to a circuit?

To apply KVL and KCL to a circuit, you need to first identify all the voltage sources and current sources in the circuit. Then, using KVL, you can write out the equation for the sum of all voltage drops in a closed loop. Using KCL, you can write out the equation for the sum of all currents entering and leaving a node. Finally, solve the equations to find the unknown voltages and currents.

Can KVL and KCL be used in any type of circuit?

Yes, KVL and KCL can be used in any type of circuit, whether it is a simple series or parallel circuit, or a more complex circuit with multiple loops and nodes. These laws are applicable to both DC and AC circuits.

What are some common mistakes when using KVL and KCL?

Some common mistakes when using KVL and KCL include forgetting to include all voltage sources and current sources in the equations, not properly labeling the directions of currents and voltages, and not following the correct sign convention for voltage drops and current directions. It is important to double-check your calculations and equations to avoid these mistakes.

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