# What is Rl circuit: Definition and 139 Discussions

A resistor–inductor circuit (RL circuit), or RL filter or RL network, is an electric circuit composed of resistors and inductors driven by a voltage or current source. A first-order RL circuit is composed of one resistor and one inductor and is the simplest type of RL circuit.
A first order RL circuit is one of the simplest analogue infinite impulse response electronic filters. It consists of a resistor and an inductor, either in series driven by a voltage source or in parallel driven by a current source.

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1. ### Why the need to be careful opening a switch on this RL circuit?

For the period before ##t=0##, during which the switch was closed we have $$-\epsilon_0+IR_1=-L\dot{I}\tag{1}$$ $$\dot{I}+\frac{R_1}{L}I=\frac{\epsilon_0}{L}\tag{2}$$ and the solution to this differential equation is $$I(t)=\frac{\epsilon_0}{R_1}+e^{-\frac{R_1}{L}t}\tag{3}$$ Thus...
2. ### How do I fix the signs in Faraday's Law in RL Circuit?

Just from looking at this circuit, we would expect the positive current to flow in a clockwise direction. Let's define the normal vector pointing out of the screen. Then the positive circulation direction is counterclockwise. I think that means that we have I am not sure about the...

15. ### Source free RL Circuit derivation

Hi, I'm struggling with source-free RL Circuit derivation. In the books in the right side diagram they've reversed polarity of inductor to get equation: V(r) = - V(L) But why? I checked google and everywhere they had put inductor with positive sign upwards. Here is what I think-- In left...
16. ### Can't find correct expression for discharging RL circuit

Homework Statement After a switch is left for a for many time constants, it is switched to b. find an expression for the total charge that passes through the resistor in one time constant Homework Equations dq/dt = I(t) I(t) = (ε/R)(e^(-tR/l)) The Attempt at a Solution so dq = I(t) dt I know...
17. ### Using Tektronix Oscilloscope to Measure Phase

Hi guys, I am working on a project that involves measuring the phase angle between two sinusoidal voltages. The circuit under examination is an RL type (the resistor was in series with the inductor), where the phase of voltage across the inductor is measured relative to the voltage input of the...
18. ### Engineering Energy Dissipated in an RL Circuit

Homework Statement In the circuit shown in (Figure 1) , the switch makes contact with position b just before breaking contact with position a. As already mentioned, this is known as a make-before-break switch and is designed so that the switch does not interrupt the current in an inductive...
19. ### Exponential forcing function to an RL circuit -- poles & zeros

For reference: Engineering Circuit Analysis, Hayt & Kemmerly, 4th ed, 1986, page 345. Given a series RL circuit, the phasor current is I(s) = Vm/(R+sigma L), where S = sigma, w (omega) = 0. Thus we are dealing with only a exponential forcing function. Obviously I(s) goes to zero as sigma...
20. ### Engineering Model of RL Circuit using the Energy function

Homework Statement From the textbook: We define an energy function $$V(\textbf{x},t) \leq 0$$ for the system $$\dot{\textbf{x}} = \textbf{f}(\textbf{x},\textbf{u},t).$$ The function V may be the total energy of the system, or it may be...
21. ### Dealing with two circuits connected by adjacent inductors

Homework Statement Here is the problem: Homework Equations Typical RL circuit equations. The Attempt at a Solution My main question with this problem is figuring out what to do with the third resistor, the one on the right. Initially, I thought of using RL circuit equations with the left...
22. ### MHB Why Do Circuit A and Circuit B Show Different Current and Voltage Behaviors?

as you can see In the image I provided I have derived the equation for i(t) and v(t). On circuit A I use a passive sign convention(current flowing from positive to negative) on the inductor, hence the equation and their corresponding graph. i(t) is decaying exponentially, v(t) is decaying...
23. ### Why Do Circuit A and Circuit B Show Different Current and Voltage Behaviors?

as you can see In the image I provided I have derived the equation for i(t) and v(t). On circuit A I use a passive sign convention(current flowing from positive to negative) on the inductor, hence the equation and their corresponding graph. i(t) is decaying exponentially, v(t) is decaying...
24. ### Source Free RL circuit confusion

1. The problem statement, all variables, and given/known data I have a single loop RL circuit with no source. I am given the the inductance of 3mH, as well as that energy storage is as follows 1 J @ t=0 and 100mJ @ t=1ms. No current is given. I have to find R. I don't need the answer just some...
25. ### Voltage across switch in LR circuit as switch is opened?

1. I thought that when switch was closed, voltage at the right side of switch was 0 and long time after the switch is open, the voltage at the right side of the switch becomes 0. 2. After the switch is open ecause of the inductor, voltage at the right side of the switch is εL = induced emf So...
26. ### Engineering Writing mesh equations for a RL circuit

Homework Statement Write the equations for the two mesh current i1 and i2. The circuit and the answer to mesh 1 are showing below Homework EquationsThe Attempt at a Solution My answer came out to be the same as the answer key except for the -25di1/dt term. It seems that this term gets...
27. ### Engineering RL Circuit Power Computation: What Am I Missing in My Solution?

I'm having some problems understanding why my computation deviates from solutions. I thank in advance to anyone who can give me some tips where I've gone wrong. Homework Statement Compute real power on resistors ## R_1 ## and ## R_2 ## and reactive power on inductor ## L ##. Circuit is powered...
28. ### RL circuits - finding resistance and inductance

Homework Statement I am practicing questions from the book in preparation for an exam, and I am having trouble with this one Homework EquationsThe Attempt at a Solution According to my professor, the answers are: R1=12ohm, R2=9ohm, L=34.28 H So far this is what I have done: Voc = 6V τ = 20/7...
29. ### Engineering Find current in circuit (DC RL circuit with switch)

Homework Statement Initially switch is at 0. At t = 0 seconds switch is put at 1. After 1 time constant switch is put at 2. Find equation for current for t > 2[/B] Homework Equations current through inductor tries to remain constant. i(t) through inductor in series RL circuit is i(t) = [...
30. ### I Understanding the Rise of Current in DC RL Circuits

Hi, I can't figure out what is the physical reason behind the fact that, in DC RL circuit, for example, the series one, the current rises from zero (supposing state zero response), to its maximum value given by ohm's law. I've understood it mathematically but I can't physically explain why...
31. ### Need help in step response circuit diagram

This isn't a homework question! I posted the question for context purpose. So I understand that at t>0 the switch moves to b. Hence the first circuit diagram (pictured) I understand. However for the 2nd circuit diagram (picture 2) when asked to transform to s domain. Why does this answer...
32. ### I Why Does an RL Circuit Use a Negative Sign in the Inductor Term?

Sorry this is the first time i come to this forum. Why the -Ldi/dt in the left side is minus but not plus sign i got confused Does everyone can help me in this problem thank you ------------------------------------------------------------- i know V-Ri-Ldi/dt=0 is true in the right hand...
33. ### How Did They Calculate Vo in the Circled Step?

Homework Statement http://imgur.com/ZKiCbbA http://imgur.com/a/ccGTV Could someone explain me what happened in the step that is circled in red please? I would appreciate it. did they multiply i0x(iL)? Homework Equations they got iL by using iL=iL(initial)*e^-t/Tau . How did they get Vo? what...
34. ### Engineering RL Circuit Confusion: Solving Homework Equations

Homework Statement Homework Equations V=IRThe Attempt at a Solution This problem is really confusing me. For VL(0-) and IL(0-), the voltage and current when t<0, wouldn't both those values just be 0? the 0- means before the switch is closed right? So before it is closed the right branch...
35. ### Engineering RL circuit Q. I must be missed something simple

Homework Statement Homework EquationsThe Attempt at a Solution I would show my working, but honestly, I'd really just like a hint as to how to begin, because I've tried multiple different things and just gotten tangled up in multiple equations that are way more complicated looking than the...
36. ### Engineering RL Circuit Problem: Find Voltage Change When Switch Closes

Homework Statement Homework EquationsThe Attempt at a Solution When the t < 0, the switch is open, the inductor acts like a short therefore the circuit looks like The current is then 20V / 4 ohms = 5 A Since the inductor has been in series with the battery for a long time, it is safe to...
37. ### Power delivered by battery in simple RL circuit

Homework Statement For a simple series LR circuit, find the energy delivered to the circuit by the battery. Homework Equations I = (V/R)*(1-e-Rt/L) P=IV E=∫Pdt The Attempt at a Solution Isn't ∫ Pdt = ∫ IVdt = ∫ (V2/R)*(1-e-Rt/L)dt = (V2/R)(t + (L/R)e-Rt/L) ? The book provides the answer, via...
38. ### Where does the current go in this RL circuit?

Hi there, I'm struggling to wrap my head around a 'should-be-simple' problem involving an RL circuit. Referring to the image I've pasted below, what happens if we were to remove switch 1, and instead created a scenario where switch 2 simply opens? Where would the current go in the inductor? I...
39. ### Engineering Impedance angle in RL and RC circuits

Homework Statement This isn't so much of a problem itself but I found it interesting that on the All About Circuits website, two of the questions give a phase angle for impedance as opposite the angle of current. I understand the current is 90 degrees out of phase with voltage in both RL and RC...
40. ### Engineering Solving an RL Circuit Analysis Problem

Hello! It's a pretty long time time since I did my last circuit analisys, so I feel a bit rusty. I have to calculate the evolution of current in the inductor: L is generic and u(t) is the Heaviside step function. Do note that at t = 0 the inductor behaves like a short circuit (I don't know...
41. ### Influence of R and L in RL circuit

Hi, I have a qualitative question about RL circuits. I'm trying to summarize how R and L each affect the transient response time L/R from the perspective of energy transfers. I'm pretty confident in my description of the influence of L. I'm not very confident in my description of R in the case...
42. ### DC Circuit Parallel: Graph Current vs. Time

Homework Statement There is a DC circuit with a resistor and inductor in parallel. Graph the current through the resistor vs time and the inductor vs. time. Homework Equations i=i(0)e^(-Rt/L)+V/R(1-e^(RT/L) The Attempt at a Solution My first thought was that initially current through the...
43. ### Engineering Solve RL Circuit Problem: Homework Statement & Equations

Homework Statement The attachment shows the circuit in question. Pardon the crude drawing. The top circuit is the circuit drawn in the text. The middle circuit is how the circuit is supposed to behave for t < 0 (switched closed). The bottom circuit is how the circuit is supposed to behave for t...
44. ### Voltage in RL Circuit Series: Why?

Suppose there is a circuit consisting of a battery, a resistor, and an inductor, and that there is initially no current. As current is increasing, the inductor creates an induced current in the opposite direction. I am confused as to which end of the inductor is at a higher voltage. Since the...
45. ### Finding the current Io for t>0 in a RL circuit

Homework Statement For the circuit in the attached file, find io (current) for t>0 Homework Equations The Attempt at a Solution I have included an attachment which shows the solution. However, I will copy the solution here as well for reference: When t<0, the switch is closed, the inductor...
46. ### Examining Voltage Response of a RL Circuit at t > 1ms

Homework Statement (see figure)[/B] The switch is initially open for a long time. At t=0 it is closed, and after 1ms it is reopened. Find the voltage across Resistor 2 at (i)0<t<1ms and (ii) t>1ms. Homework Equations V0=120V R1=500 Ω R2=125 Ω Inductance of the inductor = 0.2 H The Attempt at...
47. ### Finding the equivalent resistance of an RL cct & step input

Homework Statement Determine the inductor current i(t) for both t<0 and t>0 for the circuit shown in the attached document"Circuit 1. Homework EquationsThe Attempt at a Solution Before t=0, i=(25)/(3+2) = 5A After t=0, i(t)=i(0)e^(-t/tow) tow=L/R=4/(6/5) However, the...
48. ### Phase Difference between Voltage and Current

Homework Statement The circuit above has a 29 resistor and a 11.1 mH inductor. Calculate the theoretical phase difference between the current CPA and voltage VPB if the circuit is driven by a sinusoidal voltage source with a peak amplitude of 3.5 V at the following frequencies: 20 Hz 420 Hz...
49. ### Engineering Basic RL circuit -- Power example

Homework Statement A simple RL circuit in series connected to a source with V(t) = 30Cos(3t+75°)V and is delivering 14.12 W of power. I'm also given the power factor which is pf=0.857 and is lagging. Find the values of R and L Homework Equations P=Vm*Im/2 * pf for power theta =...
50. ### Engineering RL Circuit Transient Analysis: Simple Circuit Homework with Equations

Homework Statement Homework Equations iL = (iL(0) + Vs/R)e(-t/τ + Vs/R The Attempt at a Solution When the switch is closed before t=0, v(t) = 100V as the first 100Ohm resistor is shorted and L acts as a short wire in DC steady state. When the switch opens, v(t) = 50V by voltage divider...