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Questions tagged [kirchhoffs-laws]

Kirchhoff's circuit laws deal with the conservation of charge and energy in a circuit.

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How is voltage divided between two reverse-biased ideal diodes?

Suppose we have two identical ideal diodes (without any resistance or voltage drop). We connect these two diodes in series, in the same direction, and reverse-bias them with voltage V. Now we have two ...
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Transistor circuit driving me insane

Consider the following circuit: Now I'm asking to impose the base current as zero and $$R_C=452.35 \Omega $$ Now I have a lot of issues with this circuit because I can't find a systematic way to ...
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Solving the MOSFET, using KVL?

The question is Find VD and ID? The FET has Vth = 1.0 V and k(w/l)= 1.0 mA/V2 and λ = 0, VDD = 5 V. My question is can I use KVL like this Vdd - R1 ID - R2 ID - R3 ID =0 rearranging for ID = 11/5? ...
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Can't understand a given answer about a 1st Kirchhoff's law question

I am currently studying the textbook "Lectures about the fundamentals of Electrical Engineering" by Adalbert Prechtl and after finishing the theory about Kirchhoff's law, I tried to solve some basic ...
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How do we get the negative voltage input value of this Op-Amp?

This is an exercise we did in class about the linear limitations of an Op-Amp, I get how we get the conductance and the Current value. But I don't understand in this KVL how did we get the value of $$...
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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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1answer
44 views

What is the best approach to calculate the transfer function of this RC circuit?

I want to calculate the transfer function of the circuit below. I tried to calculate the equivalent impedance of each block and work my way with voltage dividers until I get to V3, but this method is ...
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1answer
74 views

Kirchoff law exercise

I need to determine the current across the 4 ohm resistor (name it I1). What I calculated, thought out so far : Current of 2 ohm resistor : I=5V/2ohm=2,5A. I Think this current is flow towards the A ...
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1answer
31 views

How can I solve for impedances if given RMS currents?

Given a very simple circuit such as this. If I where given the RMS values for the three currents, how could I go about solving R and Xl? (the resistor and inductor in paralell) I know I can not ...
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Use the superposition theorem to calculate Ib and Ir

What I did was first substitute Ia by an open circuit. Then applied KCL to show that Ib = Ir = Iaux, and KVL to show that Ub - RIr + KIb = 0 <=> IAux = -5 mA Then I substituted Ub by a short ...
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1answer
42 views

Calculate the Norton Resistance and Current and the Thevenin Voltage of the following circuit

U=10 V, R=10 ohm I calculated the resistance as such: 1/Rt = 1/R + 1/R <=> Rt = R/2 = 5 ohm To calculate the voltage I did KVL as such: U - 2Ur = 0 <=> Ur = 5V, where Ur is the voltage in the ...
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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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1answer
59 views

Transistors, explanation of current gain

At this first picture i have a NPN transistor with Beta=75, 2N222A transistor, both Inputs are 5V. it was very simple to calculate the current that will flow through the LED. as it is simply I1 * Beta ...
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1answer
55 views

If we have four grounded nodes in a circuit, can we connect two of them together and forget that those two were grounds?

Refer to the image attached. I personally think the answer is no because it is not necessary for the currents through both the grounded capacitors to be the same in the upper circuit, but that is not ...
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i don't understand the KVL solution to this question?

this is part of the solution of a previous exam and there are some things i don't understand about it 1- why did he assume the value of current at the 12 Ohm resistor to be 0.5A without any ...
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1answer
70 views

Find potential difference between nodes A and B in circuit below

By KVL and KCL Ix = 4A and Iy=Iz=6A The potential difference between A and B = Va - Vb = 6 +8Ix =38V I don't understand how we calculated the potential difference using KVL and KCL
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LED's brightness difference in these 2 circuits

I have past exam's problem as follows. Suppose there are circuit A (left image) and B (right image). The question is why LED in circuit A is brighter than in B. The solution states that the Low-level ...
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1answer
50 views

Is this equation wrong?

I have a trouble in understanding one of the current equation in the following example: https://www.circuitlab.com/textbook/dependent-source-feedback/ To me i3 = (Va - Vb)/R2 which yields: Va - Vb ...
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1answer
124 views

Analyzing a constant current source

I'm looking at some old chemistry education literature where a constant current source was proposed (J. Chem. Ed. 1969, 46(9) p613, link). I am trying to better understand the circuit and could use ...
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Basic KVL question

I'm trying to derive the output resistance of a common-source MOSFET with source degeneration. Are my KVL equations correct? I feel like it's very wrong.
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1answer
110 views

Confused about KVL / KCL / ohm's law

I am confused about when to use KVL/KCL or ohm's law to solve the circuit question? I need to compute voltage in point B and point C, every current pass through R1 R2 R3 R4 R1= 100 ohm, R2=300 ...
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How do you write the system of equations that solve the nodal voltages for this circuit?

I have the circuit below drawn on a piece of paper. I am trying to figure out the unknown nodal voltages x1-x9. Actually, from the circuit we already know x8=9 and x9=0. Here is my thought ...
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1answer
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Kirchhoff's Law - Finding i in non series/parallel circuit

I am trying to solve this setting up equations to each node. Node A: 10A + i5 = i Node B: i + 4A = i3 Node C: i3 + i2 = i4 Node D: i1 + i4 = i5 I am lost from ...
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1answer
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Ultra simple circuit (2 Resistor, 1 Voltage, 1 Current): Kirchhoffs Laws don't give the solution; Superposition, but how?

I am doing a course on Coursera "Intro to electronics" as electronics always was my weak point. Now we discuss npn transistors and I have simplified circuit diagram (see below) where I am supposed ...
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1answer
62 views

How do I determine the unknowns for this equation?

Suppose a series RLC circuit in series with a 12 V battery and a switch initially opened. R = 100 Ω, L = 100mH and C = 10uF. L and C are initially discharged. A t=0 the switch is closed. I want to ...
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1answer
167 views

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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1answer
45 views

Voltage drop across resistor

To find the potential difference between the points A and B: On applying KVL between A and B, why we do not consider the voltage drop across the 10ohm resistor?
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1answer
45 views

Direction of current in a LR circuit

Assume the easiest circuit with a voltage source U(t), a inductor L and a resistor R in series. The voltage source is function of time. We can have a differential equation: $$U=I'L+IR$$ But the ...
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1answer
50 views

Trying to calculate Vae by Kirchhoff KCL

I have this circuit. I am trying to calculate the voltage between A and E by using Kirchhoff current law. This is what I did. First I wrote the equation for the left side, starting at A clockwise: ...
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2answers
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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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353 views

Using mesh analysis to get the transfer function of electrical system

I am studying the book: Control system engineering for Norman S Nise. I left the college few years ago, and I forgot lots of thing about Kirchhof's laws (Voltage and current). I tried to solve the ...
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1answer
56 views

Circuit analysis, simple KVL

I have come across this example problem and can't determine the why behind why this comes out the way it does: So in figure 3.9 part a) they get 4 volts for \$v_{R2}\$, however the negative voltage ...
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2answers
80 views

Fundamentals: KVL in this AC circuit doesn't add up

I've got the following circuit: And with it the following meter readings: In the condition RL, the capacitor has a short over top of it and in RC the inductor has a short over top of it. My ...
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1answer
53 views

Find Thevenin equivalent voltage - Circuit Analysis

I am trying to understand how to calculate Vth (between the blue Volt meter and the grey volt meter). I have calculated the current correctly using KVL. However, I can't find a way to calculate Vth. ...
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Confusion with applying KCL to three phase delta connection

Below is a 3-phase delta connected for balanced loads Z: Since phase to phase voltages(voltage across loads) have 120 degrees phase differences and since the loads have the same impedance we can ...
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Kirchhoff's law when using an OpAmp

The blue text is mine and the black text is given by my teacher
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1answer
109 views

Kirchoff's Law Loop Equation Problem

This is the question I am struggling with I have found a node equation: $$ I_3 = I_1 + I_2 $$ I have found two loop equations: $$ 50 = I_3 + R_1 \times I_1 $$ $$ 50 = I_3 + R_2 \times I_2 $$ I'...
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279 views

KCL - calculating current when voltage source is present

simulate this circuit – Schematic created using CircuitLab In the above circuit, using KVL loops I'm getting the correct answer, \$ Va = 24V \$ However using KCL I am stuck at writing an ...
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47 views

Help with superposition question

Im not sure what im doing wrong the answer is 2V.
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1answer
183 views

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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2answers
128 views

How to Redraw or Interpret This

I am really stumped at this: I've been mulling this over my head for literal hours. I am pretty sure there should be 4 currents, because there are at least nodes with 3 parallel resistors. I just ...
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Kirchoffs Law for 3 Loop Circuit with Multiple Voltage Supplies

I am working on the below circuit to find; the power dissipated by RL (8Ω resistor), voltage drop across RL and current supplied by the 10 volt battery (V1). So far I have used Kirchoff's law to the ...
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Help with inductors and capacitor DC problem

SO with this question can I treat the inductors values like resistances and the inverses of capacitors values as resistances than solve the problem as if they are resistors?
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1answer
221 views

Kirchhoff's Current & Voltage Laws [closed]

What are Kirchnoff's current and voltage laws? I've tried doing some research but most explanations are quite complex. Also how can I solve the attached question using these laws??
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4answers
286 views

Confusion about KVL

I am a bit confused when it comes to Kirchoff's Voltage Law. So, I know that it states that the voltage gain in a loop is equal to the voltage drop. That makes sense as it is simply the law of ...
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370 views

Intuitive and iterative approach to understanding of blinking LED circuit

I've used following schematics to build blinking LED circuit and it worked. I tried to understand how it works qualitatively without solving differential equations. By this I mean understanding ...
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89 views

Nodal Analysis - Finding voltage given the network

My attempt to solve: I = 10A i1 = ?? i2 = ?? i3 = ?? ix = ?? Using KCL @Node 1: I = i1 + i2 @Node 2: i2 + 4ix = ix @Node 3: i1 = i3 + 4ix Applying current definitionsf 10 = (v1 - v3)/2 + (v1 - ...
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Beginner Question about the logic behind Ohm's Law?

In all the physics i learned and practiced many subjects But understanding Ohm's law used to be a big problem for me... Here is what i mean : We have a 5 volt battery. And a 3 volt/ 20 mA led. So ...
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4answers
477 views

Why the current entering and leaving the battery in an electric circuit needs to be same?

When somebody applies Kirchhoff Laws to the circuit consisting more than two batteries, the current leaving the battery is as same as entering the battery. I have no problem understanding the ...
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\$ V_o \$ in this simple circuit with 2 diodes and 3 batteries

Take \$V_{d (on)}\$ to be 0.6V for simplicity. What's \$V_o\$? Is it voltage across 1K Resistor? So... what's the direction of current flow in the 1k resistor? Is it away from BAT3 towards \$V_o\$? ...