# What is Rc circuit: Definition and 395 Discussions

A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors. It may be driven by a voltage or current source and these will produce different responses. A first order RC circuit is composed of one resistor and one capacitor and is the simplest type of RC circuit.
RC circuits can be used to filter a signal by blocking certain frequencies and passing others. The two most common RC filters are the high-pass filters and low-pass filters; band-pass filters and band-stop filters usually require RLC filters, though crude ones can be made with RC filters.

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1. ### Why can we add impedances in series?

As far as I understand, impedance is defined as the proportionality constant between complex voltage and complex current. Let ##V_c(t)=V_0e^{i\omega t}## be complex voltage. Again, as far as I understand, the actual (real-world) voltage we observe is a real number. Thus, this real-world...
2. ### Why do the headlights on the car become dim when the car is starting?

Suppose we have 12V battery. Though I can solve electric circuits, there are some very simple practical concepts that are gaping holes in my knowledge. What does it mean for a circuit device to "pull a lot of current"? What is a simple circuit element that when I connect it to the battery it...
3. ### RC circuit solution to a current pulse input

TL;DR Summary: A current pulse of amplitude I is applied to a parallel RC combination, plot to scale waveforms of the current ic for the cases a.tp < RC b. tp = RC c. tp > RC Are the calculations and waveforms correct?
4. ### What determines the time constant in a parallel R and C circuit?

If i have the R and C circuit in parallel, the battery voltage is completely applied to the capacitor of 10uF since it is in parallel, but as per the capacitor behavior it shall charge slowly. So which is correct? I mean is it wrong connection?
5. ### Determining Current Direction in a Charging RC Circuit

After the switch is closed, current flows clockwise from the battery to resistor R1 and down through the switch. I don't understand the reasoning for the following: the current from the capacitor flows counterclockwise and down through the switch to resistor R2. How do I determine the direction...
6. ### Engineering RC circuit where source depends on capacitor current

I did a kvl loop and got V + 5Io - 15 Io = 0 So, V = 10Io Then, substituted dq/dt for Io and q/c for V I get to dq/dt - 50000q = 0 solving this equation i get q = C x e^50000q (c for constant) my Io = dq/dt so Io now is 50,000Ce^50000q now my Q(0) is 3 x 10^-5 So my Io (0) should be...
7. ### I Electronics experiment boards -- What experiment can I do with these?

I recently got these electrical experiment boards to do some experiments but I am new to doing experiments with such boards. Can someone help? Thanks in advance https://ibb.co/zXTbNby https://ibb.co/tDjKrV0 https://ibb.co/JdCTgqY https://ibb.co/DDkGjbp
8. ### RC Phase Shift Oscillator not Oscillating

Hello everyone. I am having some trouble with an RC phase shift oscillator that I built as a hobby project. I am completely stuck on this and I just cannot figure it out. My oscillator is not oscillating. Here is the circuit that I am trying to get to work. Taken from...
9. ### Engineering Frequency Response Between 100Hz and 100kHz

So am trying to find the Frequency response of a RC LPF between frequencies 100Hz-100kHz ,but i don't know what formula to use .
10. ### Calculate the impedance in this RC circuit

So Z = sqrt[ R^2 + (1/wc )^2] and V=Ecos(wt) so I= Ecos(wt) / sqrt[ R^2 + (1/jwc )^2] but how do I use this to find the amplitude and phase of the current?
11. ### Engineering Step response of RC circuit with independent voltage and current sources

Dear PF, In the figure down below is Q7.47 which asks to determine the voltage v(t) across the capacitor for t > 0. Since it is given that V(0) = 0 there are two scenario's which is between time interval 0 < t < 1 and t > 1 according to the independent sources. For the scenario 0 < t < 1 the...
12. ### RC circuit using complex numbers

The impedance Z = R -j/wC + ##\frac{1}{\frac{1}{R} - \frac{\omega C}{j}}## But,1/wC=R So, solving this, I find: Z= 3R/2(1-j) |Z| =##\frac{3R}{\sqrt 2}## I =##\frac{V_i \sqrt 2} {3R}## Vi - IR-IXc =Vo Solving this, ##Vo = V_i -\frac {V_i \sqrt 2}{3} - \frac{V_i \sqrt 2}{3R} \frac{-j}{wC}##...
13. ### Discharge of a capacitor and current in an RC circuit

I'm having a few troubles understanding a few things about this circuit... Firstly, what does "In light of this, the potential between the resistors is ##16V##" exactly mean? If current isn't flowing, how could there be a potential between resistors? Secondly, how does current flow with the...
14. ### Time constant of a discharge RC circuit, capacity and charge

So, the only thing which came to my mind in order to solve this problem was actually to write down the equations using the discharge function, being given two instants and their corresponding charges... but doing so I'm unable to find anything. Ideally, I'd say I should find the time constant...
15. ### Grounding a circuit through a capacitor/parallel RC circuit

Hi, I have two similar circuits. One of them is clear for me but I am not sure how the second one works. Let's start with the clear one: a parallel RC circuit, which is explained here: At time t = 0s there are zero volts across the resistor because the capacitor is fully uncharged. After...
16. ### How to calculate R1 and R2 in this RC circuit

Using the Capacitor voltage vs. time graph, I calculated the time constant τ when the switch is closed (capacitor charging) and open (capacitor discharging). I calculated τclosed = 2.5s and τopen = 3.75s. Since the resistors are in parallel when the switch is closed, I assumed that 1/Req = 1/R1...
17. ### Engineering Why Does Doubling the Time Solve the AC Transient Equation in an RC Circuit?

Here, at voltage source zero crossing, cos(2to + pi/4) =0. So, 2to+pi/4 = pi/2 This gives to=pi/8 = 0.3926s. But the given answer is twice the answer I got i.e. 0.7852s. Have I missed anything here?
18. ### Engineering Thevenin Theorem seems to not work in this 1 bit RAM RC circuit

I have a problem which consist in 1 bit RAM made of 3 MOSFETs. One of the questions is to calculate the maximum voltage that the memory element can receive. I have obtained the result by inspection (it is 4 Volts) but I'm unable to reach the same by applying the Thevenin Theorem. My...
19. ### Set up the differential equation showing the voltage V(t) for this RC circuit

Hi all. I have another exam question that I am not so sure about. I've solved similar problems in textbooks but I have a feeling once again that the correct way to solve this problem is much simpler and eluding me. Especially because my answer to a) is already the solution to c) and d) (I did...
20. ### What is the least resistance in this RC circuit?

Hello, I know that the lower the resistance the lower the charge/discharge time in an RC circuit, i.e. 5RC is about the charge/discharge time for the capacitor. But how small is the resitstance allowed to be? I'm guessing that the lower the resistance the more the circuit looks like it has just...
21. ### Discharge in a DC RC circuit and negative sign of current

Hi everyone! I'm trying to understand why when writing the differential equation of a discharging RC circuit V_C-Ri(t)=0 \to q(t)/C - Ri(t)=0 we replace i(t) with -\frac{dq(t)}{dt}. I read many threads but I don't understand the physics behind this. The usual answers I read are something like...
22. ### Find the functions of V1, V2, V3 in an RC circuit

I tried using Kirchhof's current law, and to pose the problem in matrix form as ##\frac{dv}{dt}=Mv## with## v## the vector of the ##3## potentials at nodes ##1, 2## and ##3##, and ##M## is a ##3x3## matrix. it would be enough to show me which will be the differential equations, I would proceed...
23. ### Constant Current Source in Driving an RC Circuit

Alright. So I'm getting two different solutions depending on how I look at this problem, and I know one is correct but I don't know why the other would be incorrect. So, given this general circuit of a constant current source driving an RC circuit in parallel: Now, what they tell me in class...
24. ### Correct statement about series RC circuit

Homework Statement The battery is disconnected from a series RC circuit after the capacitor is fully charged and is replaced by an open switch. When the switch is closed, a. the capacitor does not allow current to pass b. the current stops in the resistor c. the potential difference across the...
25. ### Energy dissipated in the resistors in a 2 mesh RC circuit

Homework Statement Hi mates, I have problems solving the third part of this exercise, I've already done all the previous calculations. Given the following circuit, where the switch S is open, the power supply = 50 volts and: The initial charge in the C capacitor: QC = 0 coulombs The initial...
26. ### Time constant for parallel RC circuit

Homework Statement Question 6. Homework Equations Time constant = RC The Attempt at a Solution I think answer should be 1/2 RC as Rnet = 1/2R and to convert it to single resistance form we should first find Rnet But the answer is coming out to be RC . How? << Corrected Image added by...
27. ### Engineering Find the time constant for this RC circuit, help please

Homework Statement Homework EquationsThe Attempt at a Solution
28. ### RC circuit - Rate o'energy dissipated = rate o'energy stored

Homework Statement 1. A 2.01 uFcapacitor that is initially uncharged is connected in series with a 6.51 kΩ resistor and an emf source with 74.6 V and negligible internal resistance. The circuit is completed at t = 0. b) At what value of t is the rate at which electrical energy is being...
29. ### RC Circuit - Rate energy is dissipated in the resistor

Homework Statement 1. A 2.01 uFcapacitor that is initially uncharged is connected in series with a 6.51 kΩ resistor and an emf source with 74.6 V and negligible internal resistance. The circuit is completed at t = 0. a) Just after the circuit is completed, what is the rate at which electrical...
30. ### Engineering RC Circuit/Node voltage question

Homework Statement Homework Equations The Attempt at a Solution So you need to find the voltage across node D while the capacitor is charging, so it is going to be related to the voltage of the capacitor, so a function of time, so you need to come up with the equation for Vc(t), which I...
31. ### Calculating Charge and Time in a Discharging RC Circuit

Homework Statement RC circuit, with a resistor, capacitor and a switch with ΔVC =80V R=1.5MΩ C=22μF The switch is initially open. The switch is closed at t=0 (a) What is the charge in the capacitor when the current is 33μA (b) How times does it take for the current to reach 33μA...
32. ### Entropy change in an RC circuit

Hello,I would like some help for a problem Homework Statement Initially:At t=0 [/B]the cylindrical capacitor of capacitance c=\frac{\epsilon s}{d} (d the distance between the 2 electrodes and s their surface; \epsilon = \epsilon(T) is the dielectric permittivity) is discharged and we close the...
33. ### Need help finding current on RC circuit

Homework Statement In the circuit shown in the figure each capacitor initially has a charge of magnitude 3.60nC on its plates. After the switch S is closed, what will be the current in the circuit at the instant that the capacitors have lost 80.0% of their initial stored energy? the shown 3...
34. ### Finding R(t) in discharging RC circuit

Homework Statement A charged capacitor with capacitance C is being discharged through a variable resistor that has its resistance dependent on time: R = R(t). Find function R(t) if the current through the resistor remains constant until the capacitor is completely discharged and the resistance...
35. ### RC Circuit with parallel resistor

Homework Statement A circuit contains a capacitor of capacitance C, a power supply of emf E, two resistors of resistances R1 and R2 , and a switch S2 . Resistor R1 is in series with the power supply and R2 is in parallel with the capacitor and the power supply. S2 switches the branch that...
36. ### Solve RC Circuit Problem: Find Time of Current > 50mA

Homework Statement Suppose a 120 micro-farad capacitor from a camera flash unit retains voltage of 210 V when an unwary student removes it from the camera. If the student accidentally touches the two terminals with his hands, and if the resistance of his body between his hands is 1.8...
37. ### Discharge in a DC RC circuit and Kirchhoff's Loop Rule

Hi all, I think this issue periodically resurfaces in PF. I have found a similar discussion in this closed post and possibly others. I'm posting this because I'd like to check my understanding, if anyone is available to provide some furtherinsight. So I'm trying to gather a "overall"...
38. ### Engineering Transient RC Circuit (got answer in s but not in t-domain)

Homework Statement Homework Equations Vc = ( Initial Voltage - Final Voltage ) e(-RC/t) + Final Voltage 3. The Attempt at a Solution I got the answer through Laplace but am not getting through time domain analysis. Given q across C is 2.5mC C = 50micro F q = CV So V = 50V Initial voltage =...
39. ### Understanding Charge Flow in RC Circuits: A Scientist's Perspective

I have a RC circuit which also includes a battery, the capacitor has some charge initially before we put all the components in the circuit. Now as I connect all of them then charge will start to flow, but wheather this charge will be the sum of initial charge on the capacitor and the new charge...
40. T

### Current at Resistor 2: How to Calculate using Capacitor Voltage and Ohm's Law

Homework Statement In Fig. 27-66, R1= 10.0 kΩ, R2 = 15.0 kΩ, C = 0.400 µF, and the ideal battery has emf E = 20.0 V. First, the switch is closed a long time so that the steady state is reached. Then the switch is opened at time t = 0. What is the current in resistor 2 at t = 4.00 ms? This is...
41. ### Engineering Current Through a Capacitor in a RC Circuit

Homework Statement Find ##i(0^+) ## and ##i(t), t≥0^+## Homework EquationsThe Attempt at a Solution [/B] I'm having trouble finding the current through this capacitor. I tried using a KVL loop for ##t=0^+##, but I'm doing it incorrectly or something. Earlier in the problem I found...
42. ### Engineering Laplace Transform on RC circuit

Homework Statement Homework EquationsThe Attempt at a Solution I'm kind of lost now, how do I go about getting this into the right form for partial fraction exapnsion. And also what do I do with the V(0'). There was no information given about it.
43. C

### RC Circuit: 20V AC Source, 12V Voltage Across R, What about C?

A 50Hz AC source of 20V is connected across R and C. The voltage across R is 12V. The voltage across C is?
44. ### Solve RC Circuit Problem 1: V=IR, Q=CV

1. 2. V=IR, Q=CV3. To calculate the current in the circuit in the case when the switch is open and steady state is reached, I assumed that no current will flow "across" the capacitors and so the current I will simply be emf/(r+R1+R2) = 12 V/(1+3+2) = 2 A. The voltage drop across r would be...
45. ### RC circuit -- finding the charge on each capacitor

Homework Statement I have to find the charge ##q## on the capacitors (all have capacity ##C= 4 \mu F##) and ##\mathscr{E} = 12 V##, ##R=50 \Omega##Homework EquationsThe Attempt at a Solution I wrote the nodes current equations ##\begin{cases} i_{1}+i_{2}=i_{3}\\ i_{3}=i_{4}+i_{5}+i_{6}\\ ...
46. ### How Does a Capacitor Charge to Negative Voltage in an RC Circuit?

Homework Statement At initially, the switch is open meaning there is no current flowing. So how does the capacitor is initially charge to -5V? and what does a negative voltage capacitor means? I thought it is only when the switch is closed (t=0) that when the capacitor is being charged...
47. ### Capacitor Voltage Equations: Explained

Homework Statement Hi, I've run into two different equations for the voltage of a typical RC circuit, one resistor, and one capacitor. Please explain the different between the two. One has a 1 - the natural log and the other one doesnt. Homework Equations 1. V(t) = Vo*e^(-t/RC) 2. Vc =...
48. ### Final charge on capacitor for an RC circuit

Homework Statement Homework Equations ##q = CE(1 - e^{-t/RC})##The Attempt at a Solution I assumed that, since the problem specifies that sufficient time has passed, it meant to say that enough time passed. thus making the exponential term in the equation go down to 0, and the charge in the...
49. ### Engineering Solve Series RC Circuit for Capacitance & Currents

Homework Statement Three lamps are rated 110 V, 60 W. They are connected in parallel and a capacitor is connected in series with the group. The circuit is then connected to a 230 V 50 Hz power supply. Detremine: a) The capacitance which is required to provide the correct voltage across the...
50. ### Engineering Finding Phase Difference in an RC circuit

Homework Statement Homework Equations ##V = ZI## ##Z_R = R## ##Z_C = -\frac{j}{\omega C}## ##Z = \sqrt{R^2 + (\frac{1}{\omega C})^2}## ##P_{av} = \frac{1}{2}V_m I_m cos(\phi)## ##\phi = arctan(\frac{-1/\omega C}{R})## ##\Delta \phi = \phi _1 -\phi _2## The Attempt at a Solution I've found...