Questions tagged [kirchhoffs-laws]

Kirchhoff's circuit laws are important for circuit analysis. There are two laws: Kirchhoff's Current Law (KCL) and Kirchhoff's Voltage Law (KVL). KCL states that the sum of currents flowing into a node is zero, and KVL states that the directed sum of voltages around a closed loop is zero. Consider also using the "circuit-analysis" with this tag.

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How does the current know how much to flow, before having seen the resistor?

With the following circuits as examples : and How will the current I know how much to flow? Would any other wave travel first in the circuit and then come back ...
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7 votes
4 answers
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Can two voltmeters connected to the same terminals show different values? Circuit with induced EMF

The circuit shown below consists of two resistors connected in series that form a closed loop. No electrical sources are in that loop.Let’s assume that the resistance of the wires that connect the ...
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3 answers
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Do all components obey Kirchhoff's Current Law?

Kirchhoff's Current Law states that the net current through a node is always 0. AFAIK this derives from conservation of charge principle. My question is, is KCL applicable to any electrical component? ...
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Kirchhoff's Current Law at the ground node?

Can one do KCL at the ground node? Does any current go into the ground? I think not, but I am not sure. Bonus Question: If yes, then how does grounding buildings drain the current into the Earth?
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12 votes
5 answers
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Basics of Transistors

something has been bothering me for awhile. When I look at a circuit involving anything more complicated than RLC components (and perhaps op-amps) I struggle to figure out what it's doing unless its a ...
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12 votes
4 answers
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Does this experiment show that Kirchhoff's Law hold when there's a changing magnetic field involved in a circuit?

In this video, the electrical engineer and youtuber Mehdi Sadaghdar (ElectroBOOM) disagrees with another video from professor Walter Lewin. Basically, professor Lewin shows in an experiment that if ...
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6 answers
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Circuit yields a peculiar contradiction between KCL, KVL and Faraday's law

I don't know if this particular circuit/loop is covered in another question but I stumbled upon a video where a peculiar consequence occurs for the following circuit: For the above circuit loop ...
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2 votes
1 answer
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Voltage divider bias (BJT) leads to a huge voltage drop across the collector resistor. Why?

I've already looked for similiar questions, but couldn't find any. Basically, I'm new in electronic circuits analysis and, after following my professor's lecture and looking on the internet I found ...
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3 answers
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Why does the voltage drop across an LED matter when determining an appropriate resistor value?

In determining the voltage dropping resistor, why is the forward voltage of an LED deducted from the supply voltage instead of considering the supply voltage alone?
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1 vote
2 answers
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Converting a schematic into a graph

I've been working for some time trying to figure out how it might be possible to translate a schematic into something like a node graph, where each node is a component. I've taken some liberties in ...
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1 answer
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Mesh Current Polarity, Equation Setup

Practicing Mesh Analysis I came across this problem and te answer is really alluding me and I believe is just one polarity that I'm not understanding, the problem is the following... Vs​=10V, R1=...
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Kirchoff law circuit exercise [closed]

Hi I am starting to study electronic circuits and I found an exercise with this circuit. Now, I don't really care about the numeric results, I care more about understanding how to solve this kind of ...
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3 answers
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Solving an ideal opamp-circuit leads to a contradiction

Well, I am trying to analyze the following circuit: simulate this circuit – Schematic created using CircuitLab When I use and apply KCL, I can write the following set of equations: $$ \begin{...
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4 answers
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Kirchhoff's Laws and Circuits?

I just started circuit analysis today and learn't about Kirchhoff's Laws. Its pretty straightforward, but in all the examples my book gives they already specify the direction of the current and the ...
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4 votes
8 answers
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Mysterious energy disappearance of capacitors

Consider a capacitor, $$ C= \frac{Q}{V}$$ To derive the energy of this device, $$ U = \int V \cdot dq$$ $$ U = \int \frac{Q}{C} \cdot dq$$ (from original capacitor equation) $$ U = \frac{Q^2}{2C}$$ ...
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Simple question: pros and cons of choosing MESH or NODE methods?

My question is about MESH and NODE methods, how I choose to use one over the other? For example if I have this circuit, my professor used the node method, but also a mesh method could be used? Why? ...
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3 answers
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Finding current using Kirchoff Law, but getting unsolvable system

Hello, the original circuit above is where I am trying to find I1, and I simplify it the figure below and assuming the following current directions. Using ...
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3 answers
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Monopole antenna: does current flow in loops?

I've been wondering for the longest time about how a monopole antenna (like the one in a typical FM radio) can work without offering a return path for current. I have a hypothesis, and I'd really ...
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2 votes
4 answers
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Inverting Op Amp: Why does current flowing into output seem to magically reappear at ground?

I'm trying to understand the flow of current through the inverting op-amp circuit. I've created a simulation: The thing that is baffling me is: How come the values of PR1 (op-amp output) and PR2 (...
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2 votes
2 answers
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Mesh Analysis for circuit having Current Source

I have the following question: Since the current through the current source is not given (may be error), I assume it to be 2 A. Now since the resistors 6 Ω and 3 Ω are in parallel, I calculate the ...
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Solving this circuit using node analysis

Hi I'm having a really bad time in analyzing this I can't seem to establish the node equations, I've been reading on articles on how to solve it but the majority use current sources and the methods ...
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1 answer
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A problem with branch current method

simulate this circuit – Schematic created using CircuitLab I'm trying to solve a cicuit with using the branch current method. Here is the circuit: The words after the values are the unit in ...
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2 votes
2 answers
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Is it possible for the system of equations of an electric circuit to not have a unique solution?

When using Kirchhoff's circuit laws and Ohm's law to model the system of linear equations corresponding to an electric circuit (so far, circuits involving resistors and sources only), I haven't been ...
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2 answers
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Current direction inconsistency in Nodal Analysis

I'm very confused here! Most of the times I'm getting wrong answers or impossible equations because of this - even if I know the procedures for the analysis. It has to do with setting up nodal ...
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Two seemingly analogous cases of using Kirchhoff's current law to calculate current through a node

I'm currently studying the textbook Fundamentals of Electric Circuits, 7th edition, by Charles Alexander and Matthew Sadiku. Chapter 2.4 Kirchhoff's Laws has the following practice problems: Find ...
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How does current flow in this circuit

I'm just trying to visualize how the current flows in the following circuit. It is a follow-on question from here. The circuit is a small-signal model for a common-source MOSFET with source ...
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Output Voltage Formula verification of Operational Amplifier circuit

I'm trying to built an op-amp circuit for a PT100 temperature sensor. I've found the following circuit diagram online (from a polish website): And I'm trying to find the formula for the output ...
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2 answers
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Calculating the Thevenin Voltage of this circuit

What I did was apply kirchoff's voltage law to the closed network with the 2 resistors and the voltage source to calculate the voltage of the resistors. I got U - 2*Uresistor =0 <=> Uresistor =5V ...
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Converting a schematic to a graph

This is a follow up to the question about I posted last night, Converting a schematic into a graph. From some of the answer, I was able to re-work how the graph is done -- with components as edges and ...
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