What is Rc circuits: Definition and 88 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. A

    RC Circuits: Measuring Capacitance

    I thought that if the slope of the T versus R graph is 4.00μF, then the capacitance would be 4.00μF but it says that's wrong. I know I'm doing something wrong but I'm not sure how to approach this problem. Can someone help?
  2. wcjy

    RLC Circuit Analysis -- Two sources and two switches

    Hello, this is my working. My professor did not give any answer key, and thus can I check if I approach the question correctly, and also check if my answer is correct at the same time. When t < 0, capacitor acts as open circuit, $$V(0-) = V(0+) = 9V$$ When t = infinity, $$V( ∞) = 5V$$ (because...
  3. F

    Current is not continuous in RC circuits?

    Now that currents don't flow past the interior of capacitors at any time (charging/discharging etc), currents should be functions of a spatial coordinate, i(x), in that i(x) is non zero in wires and 0 in capacitors. But in circuits usually currents are assumed constant in the same branch. What...
  4. S

    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...
  5. R

    Resistor Grounding in a 555 Timer Circuit Explained

    Homework Statement So I am solving a 555 timer questions, and there is a resistor that is grounded on both terminals at one point. My question is what does this do to the resistor? Homework Equations Vc(t) = A + Be^(-t/(R*C)) The Attempt at a Solution I know that if you ground one terminal...
  6. R

    Equivalent resistance with a capacitor

    Homework Statement So I need to find the equivalent resistance for the following RC circuit to calculate the time constant, but I got stuck in terms of finding out the equivalent resistance. Homework Equations V = IR The Attempt at a Solution So the thing I am not sure on is how do you...
  7. M

    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...
  8. kcombs

    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...
  9. 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?
  10. unseeingdog

    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...
  11. Arman777

    I RC circuits multpile R's and C's

    I have a circuit which it looks like this. We need to write the general RC equation.Can I reduce this circuit to like ##R_{eq}## and ##C_{eq}## then solve it ? This is not a homework question.Just need theoretical approach
  12. solour

    Current Through A Resistor That Is In Parallel With A Capacitor

    Homework Statement [/B] My question is regarding part C of the question. Homework Equations V = IR V(t) = V(1-e^(-t/tau)) The Attempt at a Solution My idea is to use Kirchoff's Voltage Law and find the voltage of the capacitor as a function of time, then since the voltage across capacitor is...
  13. davidhowie34

    How to find magnetic field in a square coil next to an RC circuit

    Homework Statement 1. (35 pts) You have a coop job helping to test a capacitor energy storage system. There is a rather large capacitor with capacitance, C = 2.02F. It is charged to a potential V = 602.V with the polarity of the capacitor as shown. The large, solid line on the right of the R–C...
  14. J

    How to implement a sinewave oscillator

    Hi, I was wondering on how to implement a sinewave oscillator with a variabke frequency from 20hz to 20khz. What types of circuits are there to do this and what sort of parameters would affect the frequency range? Thanks
  15. E

    How to graph amplitude vs. frequency for a Low-Pass Filter?

    Homework Statement For my lab class my professor wants us to graph the theoretical amplitude of the output from a low-pass filter vs. frequency. I have the resistance and capacitance that I chose for the RC circuit and a V(in). Is there an equation that I should be able to use to relate these...
  16. RoboNerd

    Question on linearizing equation

    Homework Statement I posted the entire question, but I am only conserned with part B. There was a circuit drawing on there but it is irrelevant for this part of the problem. One can solve it without knowing the circuit drawing. Homework Equations The application for Kirchoff's Voltage Law...
  17. S

    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...
  18. E

    Parallel RC Circuits: Charging to 0.75V in Seconds

    Homework Statement A parallel combination of 0.1M Ω resistor and a 10 μF capacitor is connected across a 1.5 V source of negligible resistance. The time (in seconds) required for the capacitor to get charged upto 0.75 V is approximately (A) ∞ (B) ln 2 (C) log 2 (D) Zero Homework Equations...
  19. T

    Confused about solving RC circuits with nodal analysis

    Problem is in the picture below. The problem is already solved, but I am confused as to why C(dv/dt) is positive and not negative, since the current is coming out of the capacitor and towards the point v(t), which is not away from v(t) like the solution shows. But if I solve the problem with...
  20. BarelyOtaku

    Engineering RC circuits, a step skipped in solution

    Homework Statement . [/B] This is problem 7.45 in Fundamental of Electric Circuit 5th edition. 2. Homework Equations First off, I want to go ahead and say that I don't need the solution I already solved it. I went ahead and used Nodal analysis when Vs = 30. I placed a node voltage right...
  21. S

    RC Circuits, how do you solve for V(infinity)?

    Homework Statement Question is attached below Homework Equations v(t) =v(infinity) + [v(t0)-v(infinity)]e^[-(t-t0)] The Attempt at a Solution For t<0, you get the circuit where it is only Rt, R, and C, but in dc circuits, the capacitor is an open circuit, does this mean v(t0) =0? For t>0 the...
  22. N

    Engineering Coupled RC circuits with AC current source

    Homework Statement Hi, I already asked a question close to this, but now I have different conditions. This is the circuit C_1 = C_2 \\ R_1= R_2 The current is an AC , and I would like to know the voltage at R_1 and at R_2 I made some progress but I do not really know hot to continue...
  23. J

    Help understanding rc circuits?

    Help understanding rc circuits? so I know the voltage drop must be 8 v through the r1 resistor because of the 12 v charge on the capacitor. 8= r1*i and now I set up another equation 12= r2*i= 15*i and when I solve for the current I get 4/5 a but my textbook lists 3 amps as correct. Can you...
  24. P

    Understanding Phasor Analysis in RC Circuits

    I understand that the voltage phasor for a resistor is in phase with the current phasor in a simple ac circuit consisting of only an AC voltage source and the resistor. I understand that the voltage phasor for a capacitor is pi/2 radians behind the current phasor for an AC circuit consisting...
  25. P

    Understanding Phasor Relationships in RC Circuits

    I understand that the voltage phasor for a resistor is in phase with the current phasor in a simple ac circuit consisting of only an AC voltage source and the resistor. I understand that the voltage phasor for a capacitor is pi/2 radians behind the current phasor for an AC circuit consisting...
  26. S

    Confused about Kirchhoff's Laws for RC Circuits - Discharging

    Hi. When trying to derive the equation for voltage across a discharging capacitor in series with a resistor using Kirchhoff's laws, I got stuck. My attempt was that the voltage gain across the capacitor should equal the voltage drop across the resistor, therefore q(t)/C = i(t)*R, or q(t) -...
  27. L

    RC Circuits, capacitor charges and voltages

    These are 2 stand alone problems, however the answers disagree with one another and I am trying to reconcile their differences. Any insight would be appreciated! :) The answer is C. The answer provided with this question is that "there is no dependence on resistance of any kind". However the...
  28. B

    What is the voltage drop across the resistor in a discharging RC circuit?

    Homework Statement Determine the voltage drop across the resistor when the capacitor has been discharging for 10μs. Capacitance=400 pico farad and is charged to 10v through a 50kΩ resistor. Homework Equations Vr= V*e -t/CR The Attempt at a Solution Vr = V-Vc at the instant of 10μs...
  29. B

    How Does Current Behave in a Discharging RC Circuit?

    Homework Statement Determine the current flowing when the capacitor has been discharging for 5μs Capacitance=400 pico farads which is charged to 10v through a 50kΩ resistor. Homework Equations Vc = ve-t/CR The Attempt at a Solution So Vc =Ve -t/CR -t/CR =...
  30. N

    ODE for 2 RC circuits in series

    Dear all, I have problem to find the differential equation for my circuit shown in the attached picture. For input I have a current source, and the output is the voltage U (the voltage between the first and the ground node). I need the ODE to find the mathematical response of the system...
  31. PsychonautQQ

    Bode Plots in RL and RC circuits

    Hey PF! I have a test tomorrow and some of the material is on the basics of RL and RC circuits set up as high pass or low pass filters. Does a High pass filter bode plot look the same whether it's RC and RL? Same with a low pass? Can anybody to an online resource of what bode plots look like...
  32. C

    RC Circuits charging/discharging

    Homework Statement Plot I_r vs. time and Q_c vs. time starting from when the switch is moved from its lower position to its upper position. Label both axes with numbers and units. Show three time constants. Assume that the capacitor is initially uncharged. After the circuit reaches its...
  33. S

    RC Circuits: Graph Homework - Determine Flash Frequency & Voltage Sketch

    Homework Statement A simple type of blinking light circuit can be constructed using a neon lamp. The circuit has a 4.0uF capacitor in parallel with a neon lamp. When the voltage is low in the RC portion of the circuit, the lamp does not conduct electricity. Therefore, it is effectively not...
  34. K

    What is the Capacitance of a Charging RC Circuit with Known Time and Resistance?

    Homework Statement "A capacitor is being charged from a battery and through a resistor of 20kΩ. It is observed that the voltage on the capacitor rises from 10% of its final value to 90%, in 15 seconds. Calculate the capacitor's capacitance. t = 15s R = 20kΩ Vi = 10% of max Vf = 90% of max...
  35. B

    Electric Potential in RC Circuits

    Hello, At the moment, I am writing the theory portion of my lab report. In the RC circuit, will the electric potential across the capacitor be at the same electric potential as the battery? Or will it depend on the voltage drop across the intermediate resistor?
  36. A

    Engineering Help with RC circuits SPDT switch

    Homework Statement Find v(t) after t=0, when the switch moves up need to know if i did this right.. V(C1)=V(C2)=10V (this is same for t=0- and 0+) V(infinity)=0V (no voltage source) T=RC=100k(ohm)*(4uF)=0.4 sec. (i got the 4uF by putting the 2 caps. in parallel with each other, because they...
  37. K

    Engineering RC Circuits and Time Constants

    Homework Statement For the circuit below, the switch has been closed for a period of time long enough for steady state conditions to have been reached. a: Determine the time constant before the switch is opened b: Determine the time constant after the switch is closed c: Determine the...
  38. M

    Energy dissipated in RC circuits

    [b]1. You are investigating how energy is transferred in circuits with batteries, resistors, and a capacitor. First you take an uncharged capacitor and connect it in a simple series circuit with a resistor and a battery. You wait for the circuit to reach a steady state. After a steady state is...
  39. C

    RC circuits - questions about the solution

    RC circuits -- questions about the solution Homework Statement First of all , greetings from Peru and thank you to all the people who help another people here,taht's awesome , please help me with this guys... Here's the statement The solution is My questions: ok my question is about the...
  40. M

    RC circuits - Current and electric potential

    Homework Statement Given the drawing, calculate the current going through the 2Ω Resistor and then calculate the difference in electric potential from point a to b. Homework Equations V = IR juction rule: ƩI = 0 = Iin - Iout ƩV = 0 The Attempt at a Solution Well, I attempted to draw all the...
  41. J

    Mutual Inductance of Two RC Circuits?

    Homework Statement In the circuit shown in the following figure(Figure 1) the capacitor has capacitance 20 microF and is initially uncharged. The resistor R_0 has resistance 12 Ohms . An emf of 90.0V is added in series with the capacitor and the resistor. The emf is placed between the...
  42. D

    RC Circuits Voltage: Solving for V(out) with Loop Rule

    Homework Statement Relevant infor V(out) stands for the voltage divider I believe The Attempt at a Solution I am just going to get the equation first. For the first part, applying the loop rule I got 12 - 10^5q' - 10^7 q = 0 with q(0) = 0. Solving I get Q =...
  43. A

    RC circuits and potential difference

    Homework Statement Circuit is at this link: http://www.colorado.edu/physics/phys1120/phys1120_sp08/hws/capa8_figs/gian1946.gif 1. What is the potential at point a with S open (let V=0 at the negative terminal of the source, and assume it's a long time after the circuit was connected to the...
  44. K

    Optimizing Charging RC Circuits: Lowering Time Constant for Faster Charging

    Homework Statement You need to modify a simple charging RC circuit (power supply, resistor, and capacitor in series) to maintain the same maximum current but lower the the time constant and make it charge faster. Which of the following will accomplish it? A) Same R, lower C. B) Same R...
  45. S

    Voltage and Current in RC circuits

    Homework Statement A circuit includes a spark gap that connects to the ground. The width of the gap is adjusted so that the capacitor discharges to the ground each time the voltage reaches 99% of the maximum. (The circuit is basically a simple series circuit with an 80v power supply...
  46. R

    Help understanding RC circuits

    Homework Statement In a problem I have a circuit that I have not set up to know what happens as far as voltages across my battery(4v), two equal resistors and a capacitor. Homework Equations The Attempt at a Solution Because i have not seen a circuit like this I am thinking that...
  47. W

    Engineering Understanding the Role of Capacitors in RC Circuits

    Homework Statement What causes integration of V_{in} within an RC circuit?Homework Equations Z= R + X_C = R - j/(ωC) Z is the impedance of the circuit, j=(-1)^.5, ω is angular frequency, and C is the capacitance. The Attempt at a Solution I think integration is the capacitor's way of...
  48. E

    Engineering Solve RC Circuits Homework: Find Vout w/S1+S2 Closed

    Homework Statement S1 switch - always close. S2 switch is closed, until the capacitor voltage reaches 2V. given: R,C,V values. V0 = 0V. Need to find Vout while S1+S2 are closed and until S2 opens.Homework Equations Vc(t) = (Vi - Vf)*(exp -t/TAU) + VfThe Attempt at a Solution I have found the...
  49. B

    Reactive power, RL RC circuits

    Trying to understand the power network and synchronous machines, led me to the fact that I am not sure about the basics. The terms the generator is delivering or consuming reacting power made me halt. So I went back to my old course(which I allegedly passed) where the reactive power is...
  50. R

    Current after (1) time constant in RC circuits

    Homework Statement Maximum current: I max = 4.62 * 10^-4 A Time constant of circuit: T = 3.9 secondsHomework Equations T= RC The Attempt at a Solution I'm trying to find the current after 1 time constant. Seems simple enough, the current changes by 63%. So (Imax)-(Imax * 0.63) or...