# What is Kirchoff's current law: Definition and 25 Discussions

Kirchhoff's circuit laws are two equalities that deal with the current and potential difference (commonly known as voltage) in the lumped element model of electrical circuits. They were first described in 1845 by German physicist Gustav Kirchhoff. This generalized the work of Georg Ohm and preceded the work of James Clerk Maxwell. Widely used in electrical engineering, they are also called Kirchhoff's rules or simply Kirchhoff's laws. These laws can be applied in time and frequency domains and form the basis for network analysis.
Both of Kirchhoff's laws can be understood as corollaries of Maxwell's equations in the low-frequency limit. They are accurate for DC circuits, and for AC circuits at frequencies where the wavelengths of electromagnetic radiation are very large compared to the circuits.

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1. ### Solving Kirchoff's Laws: Are My Answers Correct?

Does anyone know how to do part (a). I labelled the current through R1 I1, I4 through R4, I3 through R3, I2 through R2, and I5 through the 3ohm resistor. I used Kirchoff’s Laws to make the equations I1 + I4 = 8, 2I1 + 32I3 - 14I4 = 30, and I1 + I3 - I4 = 0. I solved these equations by subbing...
2. ### Two-port linear network general representation AV + BI = 0

Hi, as follow-up to this thread I've a question about general representation of a two-port network. Basically it is ad hoc built four-terminal linear network (using controlled sources + nullator-norator pair): for it I found a general representation ##AV + BI = 0## as in the picture above. If...
3. ### Exploring Quadripole Interconnected with External Circuit

Hello, I'm struggling with the conditions under which makes sense employ a two-port 'external' representation of a quadripole (four-terminal electrical network) when interconnected to an external circuit (to take it simple assume a linear + permanent electrical network). Starting from circuit...
4. ### Mesh Analysis Method for Finding Current in a Circuit with Dependent Source

Homework Statement Find the current in each resistor. (refer to uploaded diagram) Homework Equations ##Kirchhoff's Law: I_s=I_1 + I_2## Mesh analysis method The Attempt at a Solution I'm calling ##I_s## the total current before and after the current splitting up, and ##I_1## and ##I_2## are...
5. ### Finding the Current in a circuit

Homework Statement The diagram below shows a circuit where; R1 = 5.0 Ω, R2 = 8.0 Ω, R3 = 1.0 Ω, V1 = 16.8 Volts, V2 = 1.5 Volts, and V3 = 39.6 Volts. What is the value of I1? In solving this problem, initially pick the current directions as shown. If the actual current turns out to be in the...
6. ### Kirchhoff's First Law to solve a circuit with 2 loops

Homework Statement I've recently watched a video which explains Kirchhoff's first law however, I'm not sure about his calculations. I got the same answer just wanting to make sure I am doing it right. the guy wrote L1: -75I2 +3V=0 ⇒ I2= -3/-75=0.04A He calculated L2 like -12V -125I3 +75I2=0 ⇒...
7. ### Engineering Find Currents I1 and I2 in an Electric Circuit

Homework Statement I need to find the currents I1 and I2 in the attached image, but am having some difficulties grasping the concepts. I am given E(t) = 338sin(t) as well as values for R, L and C. I think I know what I need to use but I am not sure how to put it all together Homework Equations...
8. ### Using Nodal Analysis to determine current in a resistor

Homework Statement Homework Equations ##V = IR## ##\sum_{k = 0}^{n} I_k = 0## The Attempt at a Solution [/B] I set the bottom node as the reference node and worked from there to find the three equations for the loop. When I try to eliminate ##I_4## by using ##I_4 = I_2 - I_3## I run into...
9. ### The sign of the current and voltage

I was doing the following problem: And I was asked to find Iy. I found Iy to be 2.64 using KCL. However, the right answer was negative 2.64. Is it negative only because there is a dependant voltage source with "+ -" ? And why must it be negative? Does "-" in the final answer play a...
10. ### Engineering Approach for solving voltage across a resistor in circuit?

Homework Statement I must solve for the voltage across the resistor labelled R1 in the circuit above. The values given are the resistance of each resistor, the voltage of each voltage source and the current of the current source. Note: If referring to circuit loops consider them as being...
11. ### Nodal analysis, choosing reference node confusion

I know that when we have to identify the nodes for solving a circuit with nodal analysis we always have to designate a reference node (which will be the ground node) as a reference for measuring the others' voltages. However I was practicing this and I found this example on...
12. ### Nodal analysis, choosing number of nodes confusion

Good evening people. Recently I started taking the "electric network analysis" course in my school. We already saw the mesh analysis method for solving circuits. Now we are seeing the node analysis method. I understand that the first step for this method is finding the number of nodes (and one...
13. ### Calculation of equivalent resistance

Homework Statement : [/B]Given the circuit diagram, find the equivalent resistance between points P and Q. Homework Equations : [/B]ΔVloop = 0, ΔIjunction = 0 and V = IRThe Attempt at a Solution : [/B]Eliminating the wires with no resistors and solving for resistance gives me the answer as...
14. ### Finding Voltages in a Circuit with Nodal Analysis

Homework Statement Homework Equations KCL: Σi = 0 KVL: Σv = 0 The Attempt at a Solution Using KCL: 15 = (v1)/8 + (v2)/4 Using KVL: (v1) - (v2) = (I2)R + 10 (v1) - (v2) = (I2)2 + 10 (I2) = (v1)/8 (v1) - (v2) = (2)((v1)/8) + 10 (v1) - (v2) = (v1)/4 + 10 Now there are two variables and...
15. ### Potential difference across two points in a circuit

Homework Statement [/B] Find the potential difference between points b and a in the circuit below I have already solved for the voltages of the two batteries (1 and 2) in the circuit (18 V and 7 V respectively) 2. Homework Equations Kirchhoff's Rules 1) Potential difference across any...
16. ### How do Kirchhoff's Rules apply to a circuit with multiple resistors in series?

Homework Statement [/B] Consider the circuit above. You are given the following measured values: V = 1.5 V R1 = 100 R2 = 100 R3 = 50 R4 = 50 R5 = 50 Homework Equations Kirchhoff's Loop Rule and Junction Rule The Attempt at a Solution I tried setting this up using the junction and loop...
17. ### Why Are Currents Through 3 and 4 Ohm Resistors Zero in an Open Circuit?

Homework Statement Find the value of v1, v2, vab, vbc, vca. See picture Homework Equations Kirchoff's Law The Attempt at a Solution Is it true that both current through 3 and 4 ohm resistors are zero? The way I think of this is if they aren't zero, there would be charge building up at a...
18. ### Engineering Tough Circuit Problem, Find Current When Switch is Closed

Homework Statement I got questions a) and b), but I'm stuck at c) and d). Homework Equations Kirchhoff's Loop and Junction rules. Equivalent resistance in series: Req = R1 + R2 Equivalent resistance in parallel: Req = ((R1)-1 + (R2)-1)-1 The Attempt at a Solution I really haven't gotten...
19. ### Electrical Systems Modeling (finding current and voltage drops)

Homework Statement Hello! I've been really unsure of whether my solutions to the first problem and part (b) of the second are right. My book gives few examples and so I've been trying to look on other websites for resources. Sorry if this is a lot, but any and all help would be appreciated...
20. ### Applying kirchoff's current law on transistor considering it a single

How can I apply kcl on transistor considering it as a single node since transistor can act as source or sink for electrons due to combination with holes
21. ### Understanding Op Amps and Kirchoff's Current Law

Hi I was starting to read up on Op Amps and near the beginning they said that current flowing into an Op Amp equals current going out (output current + 2 input current + 2 source current = 0) on the basis of KCL. I'm confused because I thought KCL only applied for all currents entering and...
22. ### Kirchoff's current law for an opamp

Homework Statement http://img3.imageshack.us/img3/3939/opamp.jpg Draw an imaginary boundary around the op-amp, and apply KCL at the five wires that intersect the boundary Homework Equations The Attempt at a Solution I am having quite a problem understanding the question...
23. ### Kirchoff's current law question

I'm looking at the derivation of a band pass filter circuit, and part of the circuit is a capacitor and resistor in parallel from the non-inverting input to the output. My thinking is that the current through the capacitor is going to be the current coming in (since the inverting input draws no...
24. ### Kirchoff's Law: Steady Current in Circuits

Is Kirchoffs current law basically saying the current through any point in a circuit is exactly the same and will remain the same as long as the voltage remains the same? Lets say I have a steady current running through a circuit will that current be exactly the same on one end or the current...
25. ### Kirchoff's Current Law - Negative Current Value?

First of all, sorry for the poorly drawn figure. In this figure, given are several conducting elements connecting by conducting wires, with the direction and amount of current flow indicated. I have to find the current across elements I1 through I4. When I apply Kirchoff's Current Law at node...