What is Circuit theory: Definition and 49 Discussions

A network, in the context of electrical engineering and electronics, is a collection of interconnected components. Network analysis is the process of finding the voltages across, and the currents through, all network components. There are many techniques for calculating these values. However, for the most part, the techniques assume linear components.
Except where stated, the methods described in this article are applicable only to linear network analysis.

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  1. E

    Time domain equation for RC circuit with AC input

    TL;DR Summary: How to find Time domain equation for RC circuit with AC input from inverse laplace transform For a simple RC circuit with AC input such as this: https://www.electronics-tutorials.ws/wp-content/uploads/2013/08/rc12.gif?fit=310%2C151?fit=310,226. If the AC input is just a simple...
  2. E

    Voltage gain of a bipolar transistor circuit

    For a simple bipolar transistor above, base-to-collector voltage gain ≈ -gm*Rc/(1+gm*Re) < 0, base-to-emitter voltage gain ≈ 1 > 0, should emitter-to-collector voltage gain ≈ -gm*Rc/(1+gm*Re) * 1 < 0. How come it is equal to gm*Rc > 0?
  3. ZoeDale

    Engineering Analyzing this operational amplifier circuit with DC

    Hi all, I attached my attempt at a solution in the attached picture. I am using the textbook titiled as ”electronic circuit analysis“ by David E. Johnson, and op amp is in chap 3; while I did not find any example that attach the Vee and Vcc with amplifier . It seems that v+ = v- doesn’t hold in...
  4. cianfa72

    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...
  5. cianfa72

    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...
  6. M

    Engineering Circuit theory: capacitor energy storage and discharging/charging times?

    This is not my homework. I took it upon myself to answer a textbook question for mental stimulation. I wanted to know if someone can verify if these were the correct values that needed to be solved for, process, and final answer, and if not, what needed to be considered. For the initial...
  7. cianfa72

    Circuit theory - Resistor function for dynamic non linear circuits

    Hi, I'm reading the following paper (L. Chua) about the state-of-art of dynamic non linear circuit analysis -- Chua_Dynamic_Circuits I've a doubt about Theorem 2 on section 3.2 On the Existence of the Resistor Function that establishes sufficient conditions for the existence of network...
  8. cianfa72

    Relations between ##k## Currents & Voltages for Black-Box Device

    Hi, I'm aware it is an odd question. Consider a ##k##-terminal electrical device as black-box. We know from KLC and KLV that just ##k-1## currents and ##k-1## voltages are actually independent (descriptive currents and voltages). Furthermore we generally expect there exist ##k-1## relations...
  9. cianfa72

    Circuit Theory - about the applicability of the substitution theorem

    Hi, I've a doubt about the applicability of the substitution theorem in circuit theory. Consider the following picture (sorry for the Italian inside it :frown: ) As far I can understand the substitution theorem can be applied to a given one-port element attached to a port (a port consists of...
  10. C

    Calculations for a capacitor charging from another capacitor

    Hi all, I'd appreciate help in calculating the voltages in the circuit shown. I thought it should be fairly straight forward, but it has me stumped. This is a sample-and-hold circuit for an ADC -- the switch is closed to charge the hold capacitor with the sample voltage and then opened to...
  11. rude man

    Insights A New Interpretation of Dr. Walter Lewin's Paradox - Comments

    Greg Bernhardt submitted a new PF Insights post A New Interpretation of Dr. Walter Lewin's Paradox Continue reading the Original PF Insights Post.
  12. K

    Basic Circuit Theory by Charles Desoer

    Hello, I am currently taking a circuits class and I was looking for the solutions manual for the book Basic Circuit Theory by Charles Desoer. I haven't been able to find it anywhere but I really want it to practice more of the problems. I am able to do some but I never know if they are right or...
  13. D

    Engineering Calculate the effective values in this 3-Phase Circuit

    Homework Statement Given the known quantities ##R, C, L##, ##k##, and the effective values of the voltages ##E_1=E_2=E_3=E## , ##w = \frac{1}{\sqrt{LC}}## of the direct-symmetrical 3-Phase system find the expressions for the effective values of ##U_{12}##, ##U## and ##I## and calculate the...
  14. T

    Retired Railroader Explains Easiest AC Circuit Theory

    I am retired from a major railroad co. where I worked on electronic weighing equipment. I have an associate of applied science degree from a local university. I have a basic understanding of dc and ac electricity but the explanation I recently read on this forum was the easiest to understand...
  15. F

    Complex Capacitor Circuit (for me)

    Homework Statement 1. V for C1 2. Let's Say "C" is Resistor then C1 = R1 etc. how to get Eq Resistance for this Circuit ?[/B]Homework Equations Faraday's Law, Kirchoff Law The Attempt at a Solution [/B] for no 1 :I just want to make sure. point A is transfering negative charge to C2 and...
  16. A

    Resonant Frequency and Transfer Functions

    Suppose I have some sort of a filter, whose transfer function is given by H(w), where w is the angular frequency of the input signal in radians per second. I want to know the maximum value of the transfer function. If I solve for the resonant frequency w0, which from my understanding is the...
  17. D

    V2 of two symmetrical T attenuator pads in cascade

    Homework Statement http://imgur.com/qBXvrGz Above is a sketch of the circuit, a two stage symmetrical attenuator consisting of two symmetrical T attenuator pads connected in cascade, with the values that I have worked out for the resistors. The reduction is 15dB in the first stage, and 8dB in...
  18. D

    Engineering Laplace tranforms, transient current series CR circuit

    Homework Statement A step voltage of 120v is applied to a series CR circuit. R = 20KΩ, C = 4µF 1. Deduce, using Kirchoff's voltage law and Laplace Transforms, an expression for the transient circuit current. 2. Using the equation obtained in 1. deduce the equations for the transient voltages...
  19. C

    Engineering Understanding Diode Analysis: Exploring Voltage Output in Circuit Theory

    Homework Statement Hi, In some of the diode analysis examples that we did in class, we often end up with circuits like the ones shown here. I'm quite confused because sometimes I understand them and other times I just don't know how these voltages are coming from. It really makes me question...
  20. D

    Engineering Solving Linear Circuit Homework: Calculating ΔP for Ideal Generator E1

    Homework Statement In the circuit above ##E_1=E_2=E_3##, ##Ig_1=Ig_2=Ig_3## and ##R_1=R_2=R_3=R_4##. In the case when the switched is closed the power of the ideal generator ##E_2## equals ##P_{E_2}=-30W##. Then the switch opens. Calculate the ##ΔP_{E_1}##. Homework Equations 3. The Attempt...
  21. sammyqw

    Engineering Circuits 1 help with integration

    Homework Statement http://imgur.com/a/qlQ5z Homework Equations i=i(o)+1/L integration(v0) dt formula is in the attemp at a solution. The Attempt at a Solution http://imgur.com/a/HVjl1 For the interval 2<t<infinite . I understand...
  22. Domenico94

    Understanding Equivalent Impedance in a Bridge Circuit | Homework Help

    Homework Statement Hi everyone, I'm just having a little trouble with equivalent resistance in a bridge, in the image I attached. The textbook says that the way to solve this is to put R3 and ZL2 in series, that series is in parallel to the short circuit in diagonal, and then at the end we...
  23. R

    KCL and First order circuit theory

    My question applies to the case when the switch opens. By applying KCL in order to get a first order diff equation, the following problem arises when I choose different current directions (which shouldn't happen because KCL says the current direction doesn't matter because it will be fixed...
  24. F

    Creating a Simultaneous Circuit: Exploring the Concept of Bridging Two Circuits

    Is it possible to have one part of the circuit running with electricity then manually add in a second part of the circuit to the first part and have both running simultaneously? Is there a name for such a circuit? The voltage and current of the first part of the circuit would change because of...
  25. R

    Best way to improve knowledge of electronics/circuit theory?

    Hi guys, I recently finished my Physics undergraduate degree, and will be starting my first job in September. My employers have asked me to improve my knowledge of electronics before I begin work. I would like to improve my ability to analyse and understand circuits, and also learn more about...
  26. J

    Engineering Circuit Theory Question KCL and Dependent Sources?

    Homework Statement I need to find the voltages (if any) and currents of these circuit, but particularly Io I do know that I have to use KCL bot I don't know how, can somebody help me with a node or somethinghttps://www.physicsforums.com/attachments/c2-jpg.80412/ I do not have any other info...
  27. C

    Engineering Circuit theory -- Conditions to balance a resistive bridge circuit

    1. Homework Statement Establish the condition required to make the current through Ze in Figure 1 zero (i.e. For the voltage Vx to equal Vy). Homework EquationsThe Attempt at a Solution I'm not sure if I'm on the right line here, hopefully someone can point me in the right direction if it's...
  28. D

    How does a current source work in Norton's Therom

    Hi.i know that a ideal current source has infinite resistance and it supply's constant current to aload connected across it. The current source doesn't have the infinite resistance in series to it but in pparalle. All is well until I think of this Norton's Therom. When we transform a voltage...
  29. A

    Engineering Circuit theory -- Current source, voltage source, resistor in series

    Homework Statement the voltage Vc in the figure is always equal to 2 Relevant equations The Attempt at a Solution From kirchhoffs law, -Vc+4+5=0 Vc=9 V will Vc always equal to 9 V or it will vary?
  30. A

    Engineering Circuit Theory Problem - Current and Charge

    Homework Statement P 1.2-4 Homework Equations I know that i(t) [current w/respect to time] = dq/dt. I also know that by the previous equation, q(t) = ∫i(τ) from -∞ to t (sec). The Attempt at a Solution I understand simpler problems involving finding q(t) by using the integral relationship...
  31. R

    Engineering Circuit Theory Question (KCL/KVL/Dependent Source)

    Homework Statement Here's the problem: Find the equivalent conductance Geq and then the equivalent resistance Req "seen" by the current source Is in the circuit in terms of the literals R1, R2, and gm. Figure: Homework Equations Ohm's Law: V = IR KVL: V1 + V2 + ... Vn = 0...
  32. D

    Why Does Current Reflect in an Antenna System?

    antenna circuit theory help! Im having trouble understanding vswr and current path in an antenna system. Example is the dipole...Ive read that the parasitic capacitance between the 2 wires forms the complete circuit but then I read about standing waves that reflect at the open circuit. My...

    Why does current decrease to a steady state value in a series RL circuit?

    I am under the impression that if you have an inductor and a resistor connected in series with a DC supply, that at the instant the switch is closed, the minimum current that circuit will flow, is flowing at this time? kirchoff's law for the circuit... Vsource - Ldi/dt - Ri = 0 therefore...
  34. M

    Engineering Please help me in this IES question in circuit theory (subject)

    i m trying to solve this question by method given in most of the standard books i.e. Vc(t) = Vc(\infty) - [Vc(0\hat{}-) - Vc(\infty) ] e \hat{} -t/RC first i found Vc(0\hat{}-) by considering switch open and inductor behaving like short and capacitor open at steady state...then i find...
  35. A

    Engineering Is Something Affecting the Current Flow in this Circuit Theory Lab Experiment?

    Homework Statement In last weeks lab, I was asked to find the resistance of two unknown resistors. I hooked them up in series with a 10V source and measured the current across each one. The ammeter read 5.77 mA at Rx and .014 mA at Ry. Shouldn't the ammeter have read the same value at both...
  36. G

    Engineering Ee331 Circuit Theory answers the Questions emergency?

    Can someone help me? In the attached file to resolve that one or more of the questions? When I am in a situation very difficult and very few I do not know the answers to the following questions (the problem statement?? relevant equations...) Because I am a former student at the university...
  37. R

    Engineering Mutual Inductance: Transformer AC Circuit Theory Questions

    Homework Statement http://img265.imageshack.us/img265/8616/43354308.png I have an exam coming up in a few days and I am doing some revision questions from some past exams and this is one I have attempted but I have no solutions to check my answers. The Attempt at a Solution using Vs = 12cos(...
  38. N

    Learning Power Theory Circuit Theory

    I'd like to learn about how the fundamentals of how power works and how circuit theory works, while actually keeping a continuum between the fundamentals. In otherwords, I picked up a book on circuit theory, and it was filled with rules with no physics-backed explanations. I understand some...
  39. B

    Simple AC circuit theory problem

    Homework Statement It's a simple AC circuit with a 100ohm resistor and a 10mH inductor connected in series. The voltage is given as a function rather than a quantity: V = 20sin (5000t). Problem asks to find the peak current in the circuit. Homework Equations i = integral (V/L)dt Z = sqrt...
  40. J

    Engineering Elementary circuit theory question

    it's only the second day of class but my professor assigned some problems that are those weird ones that neither he nor the book even discusses, I have tried several different methods including parametric graphing, integrating the functions, deriving the function, but to not even the slightest...
  41. A

    Electric Circuit Theory Concept

    Why do we take ideal voltage source to have 0 impedance and ideal current source to have infinite impedance. Please explain mathematically also!
  42. D

    Basic Circuit Theory: 60W Globe & Voltage Relationships

    Hey all. I've never really done anything in the way of circuit theory up until now, where i have just started a unit on introduction to electrical/electronic engineering. Lets say i have a 60W light globe. Does this mean that the maximum power it can dissipate is 60W, after which it will...
  43. E

    What is the Current in this Circuit with Given Values?

    Homework Statement I have attached the circuit diagram to this post. I have to find i which I have shown in the diagram. All the voltage and resistor values are also given. Homework Equations The Attempt at a Solution I tried finding the current for the whole circuit which would...
  44. A

    Engineering Solving a Superposition Circuit Question: Finding Ia without a Voltage Source

    http://img442.imageshack.us/img442/2070/circuit1vf1.gif i drew this from a superposition question.. the voltage source is shorted out. what on Earth could Ia be if there's no voltage source?
  45. V

    Engineering Circuit Theory Problem: Find Vx for 5A Source to Supply 60W

    Hey, I'm having a bit of difficulty with this specific circuit theory problem... We understand the basics, Ohm's law, Kirchoff's voltage and current laws, voltage and current division... I'm just confused about what to do with this problem: Find the value of Vx in the circuit below such that...
  46. K

    Circuit Theory: physics vs. convention?

    This bothers me every time I study circuits, currently introductory level. I can solve problems just fine, but something is just not "clicking" here. Mostly conventions for things like current, power absorption, etc... Is there some where an explanation of what actually happens in a...
  47. V

    Working from electromagnetism to circuit theory

    Hi, Are there ways to use/reduce electromagnetic theory to understand circuit theory better? ie use circuit theory as a special case of em theory? if so can you suggest books which do it this way? basically my idea is to look at any circuit from the general point of view - using the physics of...