# Kirchoffs Law and simple circuit problem

• QuarkCharmer
In summary, the homework statement is confusing and the attached image does not provide a clear solution.
QuarkCharmer

## Homework Statement

The problem is in the attached image. I can't figure out what is going on. The circuit as given is at the top, I have circled what I am trying to find.

## The Attempt at a Solution

I used the junction law to find the current through the 3 ohm resistor to be 8 amps. Then I took three loops of the system and applied kirchhoffs voltage law, and solved the system of three equations and 3 unknowns, but it's inconsistent. I don't see where I am going wrong but I suspect it has something to do with my loops.

No matter how I do this, it always works out to be impossible?

Thanks

I think you're overthinking this

Assign a potential of 0V to the node labeled d (make it a reference node). Then using the known currents and resistances, assign relative potentials to nodes b, h, f. Continue...

That potential of 0 volts is from which voltage source though? I'm not sure I understand what you mean exactly. I have done about 20 problems like this, finding currents and resistances and emf's without any problems just doing loops and solving. It should work?

If you mean, using node d as the "ground" if I were say, hooking up a multimeter or something, then how do you know that node d has 0 potential?

QuarkCharmer said:
That potential of 0 volts is from which voltage source though? I'm not sure I understand what you mean exactly. I have done about 20 problems like this, finding currents and resistances and emf's without any problems just doing loops and solving. It should work?

If you mean, using node d as the "ground" if I were say, hooking up a multimeter or something, then how do you know that node d has 0 potential?

It's zero because you say it is It's a point of reference, as you say, as if you were to connect the negative lead of your multimeter to it. The same thing is done when you choose a reference node for nodal analysis. The circuit as a whole has no absolute potential reference to anything external, so you're free to assign your own "zero" reference point.

EDIT: Note that your choice of loops did not include the 3 Ω resistor in any path. That's why the system of equations you wrote would not yield a consistent result. Your equations must cover every component.

Last edited:
I didn't know that you had to hit every component, but that makes sense since most/all of the variables are dependent on the others. To be clear, I need to make sure I cover all the components in my system, but that does not mean I need to do all possible loops right?
(I got the right solution now, knowing that information, thanks!)

QuarkCharmer said:
I didn't know that you had to hit every component, but that makes sense since most/all of the variables are dependent on the others. To be clear, I need to make sure I cover all the components in my system, but that does not mean I need to do all possible loops right?
Correct.

Got it, thanks Gneill.

## What is Kirchoff's Law?

Kirchoff's Law, also known as Kirchoff's Circuit Law or Kirchoff's Rules, are two fundamental principles that govern the behavior of electrical circuits. These laws were developed by German physicist Gustav Kirchoff in the 19th century.

## What are the two types of Kirchoff's Law?

The two types of Kirchoff's Law are Kirchoff's Current Law (KCL) and Kirchoff's Voltage Law (KVL). KCL states that the sum of currents entering a node or junction in a circuit is equal to the sum of currents leaving that node. KVL states that in a closed loop or circuit, the sum of all voltage drops is equal to the sum of all voltage rises.

## How do I apply Kirchoff's Law to solve a simple circuit problem?

To apply Kirchoff's Law to solve a simple circuit problem, you need to first identify all the nodes and branches in the circuit. Then, you can use KCL and KVL to write a set of equations based on the given information. These equations can then be solved simultaneously to find the unknown values in the circuit.

## What is the difference between series and parallel circuits?

In a series circuit, all components are connected in a single loop, and the same current flows through each component. In a parallel circuit, the components are connected in multiple branches, and the total current is divided among the branches. Kirchoff's Law is applied differently in these two types of circuits, with KVL being used in series circuits and KCL in parallel circuits.

## Can Kirchoff's Law be applied to any type of circuit?

Yes, Kirchoff's Law can be applied to any type of circuit, including both DC and AC circuits. However, it is important to note that these laws are based on certain assumptions, such as ideal components and steady-state conditions. In some cases, these assumptions may not hold true, and Kirchoff's Law may not provide an accurate solution.

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