What is Rc: Definition and 643 Discussions

rc (for "run commands") is the command line interpreter for Version 10 Unix and Plan 9 from Bell Labs operating systems. It resembles the Bourne shell, but its syntax is somewhat simpler. It was created by Tom Duff, who is better known for an unusual C programming language construct ("Duff's device").A port of the original rc to Unix is part of Plan 9 from User Space. A rewrite of rc for Unix-like operating systems by Byron Rakitzis is also available but includes some incompatible changes.
Rc uses C-like control structures instead of the original Bourne shell's ALGOL-like structures, except that it uses an if not construct instead of else, and has a Bourne-like for loop to iterate over lists. In rc, all variables are lists of strings, which eliminates the need for constructs like "$@". Variables are not re-split when expanded. The language is described in Duff's paper.

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  1. 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...
  2. F

    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"...
  3. Sheldon11

    I Understanding RC Band Pass Filter Graphs

    I want to know about RC band pass filter ! more specifically details about the graph of voltage vs frequency.. how the curves goes up and why the curve goes down? I don't understand ... please help me out
  4. J

    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 =...
  5. sumit_1

    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...
  6. A

    Turbo-Jet Engine for Medium RC Aircraft

    Hello , I am thinking to work on a RC aircraft ( Airplane ) that can load a small supply of Medical Firstaid in small range. So I need to make it fast and stable. So I'm thinking to use a small Turbo-jet engine in it which will be home-made. Please suggest me -- (1) Is that makes any sense ...
  7. Drakkith

    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...
  8. C

    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.
  9. V

    First Order Transients, RC circcuit response DC voltage

    So this is an example given to me in one of the guides. I am somewhat confused as to why R and R1 are considered parallel when the switch is closed at t=0. I thought that the two resistors cannot be parallel since there is a voltage source between them. One hypothesis I had was to treat it...
  10. 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?
  11. S

    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...
  12. F

    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}\\ ...
  13. A

    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...
  14. 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...
  15. F

    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...
  16. TheBigDig

    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...
  17. Y

    Can't we use dq/dt in RC discharge?

    In the derivation of discharging RC circuit, you use I = -dq/dt to get Q = Q0 e-t/RC But isn't dq/dt already implied to be negative, since charge on the capacitor is decreasing, and you force it to be negative using initial nd final conditions? So the final state is some low charge q, and the...
  18. 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
  19. D

    RC Multiloop Circuits, Find Current at Specific Time

    Homework Statement Homework Equations For a basic RC circuit during charging: q = CV(1-e-t/RC) i = V/R (e-t/RC) The Attempt at a Solution I can solve basic RC circuits but this is just out of my realm of understanding. I can also find the max charge of the capacitor. I'm not looking for...
  20. F

    Automotive How to calculate Torque on the rear wheels of an RC car?

    Hi guys, I'm working on a project where I need to find the torque produced by the rear wheels of an RC car so that I can convert it into power and then into the current required by the motor. So T=ω×Pmech → Pmech → Pelec → Imotor Here are the details for the car: 1kg weight Torque on each rear...
  21. M

    Current of RC Circuit After Switch is Opened

    Homework Statement See attached image for circuit diagram and givens. The switch has been closed for a very long time. a) What is the charge on the capacitor? b) The switch is opened at t=0 s. What current initially flows? Homework Equations V = IR Q=CV I=I0e-t/(RC) The Attempt at a Solution...
  22. BrendanKerrisk

    B RC Helicopter in a Train (Forces)

    I was talking to my Physics teacher about this at lunch. If I was to have an rc Helicopter which i had hovering perfecting (if only i had the skill) on a train at rest. What would happen in terms of the position of the helicopter as the train accelerated? Would is stay at the same point in...
  23. terryds

    Current as a function of time in an RC circuit

    Homework Statement How to determine the current as a function of time that flows in 10 ohm resistor, 100 ohm resistor, and 15 microFarad capacitor? Please help Homework Equations I = V/R I_capacitor = I e^(-t/RC) The Attempt at a Solution I only know the equation V=IR and the capacitor...
  24. terryds

    Solve RC Circuit Problem: R1=10k, R2=15k, C=0.4F, V=20V

    Homework Statement R1 = 10 kohms R2 = 15 kohms C = 0.4F Voltage source = 20 V At first, the switch is closed for a long time so that the capacitor reach its steady-state condition. Then, the switch is opened at t=0. How much does the current flow across R_2 at t= 4ms? Homework Equations I...
  25. Bassa

    Initial Voltage in an RC circuit with a Current Source and no Voltage Source

    Homework Statement [/B] Derive an expression for vc(t) in the circuit of Figure P4.13 and sketch vc(t) to scale versus. I attached a screen shot of the circuit for this problem. time. Homework Equations V = IR V = V0exp(-t/tau) The Attempt at a Solution [/B] I am trying to find the...
  26. terryds

    Calculating Charge and Potential in a Series RC Circuit

    Homework Statement An electric circuit is shown as above. The switch S is closed for a long time and the current flowing is constant. Given that C1 = 3 μF, C2 = 6 μF, R1 = 4 kΩ, R2 = 7 kΩ If the power at R2 resistor is 2,4 W a) Determine the charge at C1 b) When the switch is opened, after...
  27. M

    What is the potential at the top of R2 in this circuit?

    Homework Statement A circuit is constructed with four resistors, one capacitor, one battery and a switch as shown. The values for the resistors are: R1 = R2 = 41 Ω, R3 = 68 Ω and R4 = 154 Ω. The capacitance is C = 49 μF and the battery voltage is V = 12 V. The positive terminal of the battery...
  28. Mausam

    Capacitor question -- charging time for an RC circuit

    Homework Statement Hello everyone , this question has been troubling me for weeks,so if anyone could please help me out.i have attached the pic of the question.The answer given is 2 seconds but i am getting a different answer. Homework Equations first of all i distributed the charge on the two...
  29. C

    RC circuit black box circuit modeling

    Homework Statement I have a red mystery box which contains a 20, 50, 100, and 200,000 ohm resistor (one of each and ONLY one.) There are three terminals on the box you can plug a voltmeter into... testing A-B I got 60k, testing A-C I got 140k, and testing B-C I get 120k ohms. So this is a bit...
  30. M

    Finding Resistance in RC Circuit

    Homework Statement In a simple RC circuit the current as a function of time behaves in the following manner: I(5s) = 8.823 I(10s) = 7.788 I(20) = 6.065 I(30) = 4.724 I(40) = 3.679 I(50) = 2.865 I(60) = 2.231 I(70) = 1.738 I(80) = 1.353 I(90) = 1.054 I(100) = 0.821 I(110) = 0.639 Assuming...
  31. L

    The Minimum voltage requirement for an RC Oscillator

    Hi I am trying to run an RC oscillator using a 2N3904 (Datasheet for reference: http://www.kynix.com/uploadfiles/pdf8798/2N3904.pdf) The circuit looks like the following. I want to run it at 0-5v but I failed, I assume it is because the voltage is not high enough? What would you expect the...
  32. A

    Thevenin resistance in an opamp RC circuit

    Homework Statement In the figure given what is the Thevenin resistance between the nodes of the capacitor?? Homework Equations The Thevenin resistance is the open node resistance between two points. The Attempt at a Solution The way I see it, R2, Rf and R1 are in series and that combination...
  33. freakywarlock

    RC Oscillator Circuit Adjusting Frequency

    Hi, I am working on RC OScillator Circuit, but i had problems with adjusting frequency. I can adjust frequency but it effects amplitude too (amplitude is changing while adjusting frequency), how can i separate these two variables ? I mean, when I am adjusting frequency, I want to amplitude...
  34. H

    Discharging capacitor in RC circuit, confusing path

    Homework Statement The circuit in the figure below has been connected for a long time. Let R1 = 8.20 Ω and R2 = 4.40 Ω. (a) What is the potential difference across the capacitor? (b) If the battery is disconnected from the circuit, over what time interval does the capacitor discharge to...
  35. H

    RC Circuit and current from a discharging capacitor

    Homework Statement In the circuit of the figure below, the switch S has been open for a long time. It is then suddenly closed. Take = 10.0 V, R1 = 56.0 kΩ, R2 = 200 kΩ, and C = 14.5 μF. (a) Determine the time constant before the switch is closed. (b) Determine the time constant after the...
  36. 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...
  37. H

    How Do You Solve Complex RC Circuit Problems?

    Homework Statement In the figure below, suppose the switch has been closed for a time interval sufficiently long for the capacitor to become fully charged. (Assume R1 = 11.0 kΩ, R2 = 22.0 kΩ, R3 = 4.00 kΩ, and C = 11.0 μF.) (a) Find the steady-state current in each resistor. (b) Find the...
  38. H

    Having trouble rearranging this RC circuit

    Homework Statement Switch S shown in the figure below has been closed for a long time, and the electric circuit carries a constant current. Take C1 = 3.00 μF C2 = 6.00 μF, R1 = 4.00 kΩ, and R2 = 7.00 kΩ. The power delivered to R2 is 2.30 W. (a) Find the charge on C1. (b) Now the switch...
  39. R

    RC Circuit with a voltage source

    Homework Statement A voltage source E_0 cos ωt is connected in series with a resistor R and a capacitor C. Write down the differential equation expressing Kirchhoff’s law. Then guess an exponential form for the current, and take the real part of your solution to find the actual current...
  40. Z

    Engineering Find v(t) and i(t) in the RC circuit

    Homework Statement Homework Equations Voltage Division v2 = vs * (r2/(r2+r1)) KCL - sum of all currents at a given node is 0 V= i * r The Attempt at a Solution [/B] This is my solution...
  41. sammyqw

    Engineering DC state RC circuit Find Vc(0)

    Homework Statement Find Vc(0) Homework Equations Nodal Eq , ohms law The Attempt at a Solution Can someone please check my work for Vc(0)? I'll appreciate it.
  42. sammyqw

    Engineering RC Circuit Problem: Hi, Is Capacitor Replaced by Short Circuit?

    Homework Statement 2. Homework Equations [/B] KCL, Node Analysis , Mesh Currents The Attempt at a Solution Hi, in part b when t>0 the capacitor is replaced by an open circuit , however in part c the capacitor is replaced by a short circuit why is that?Aren't inductors the only ones...
  43. M

    Determining the capacitor value for an RC circuit

    hi, i have a question which i was hoping someone could help with,a series circuit featuring a capacitor (C) charging via a 1Mohm (R) resistor and a 12volt dc supply(VS).i know the equation to describe VC is VC=VS(1-e -t/RC)the question is: assuming VC is 2V after a time of 4 seconds, determine...
  44. T

    Engineering Problems with First order RC circuit

    I have problems with question b. I don't know where to start. If the switch is on steady state, the current through capacitor would be 0 and i can't have K. This makes me confused. This is the Total response function of a): V0(t) = K^(-1/2t)
  45. J

    Direction of current in RC parallel circut

    In the figure below in e1 1.64 why is i(t) negative. When switch is put to S1 position, the capacitor will start discharging. So current will flow from top plate of capacitor to resistor to bottom plate of capacitor. Where did negative sign come from in eqn. 1.64? When charging the current...
  46. BiGyElLoWhAt

    Optimization Problem with an RC BP filter

    I am assigned to design a circuit that peaks voltage at 10kHz and is less than half peak voltage at 3k and 30k. Only capacitors and resistors are allowed. The circuit I'm using is attached. I end up with ##I_0 = [\frac{-R_2\omega^2C_1C_2 + [C_1+C_2]R_1R_2\omega^3C_1C_2 - R_1\omega^2[C_1+C_2]^2...
  47. T

    RC circuit, finding voltage across a capacitor

    Homework Statement I am trying to find the capacitor voltage in the following picture: Find i(t) in the figure below. Assume dc steady state conditions are valid for t<=0. Homework Equations i=c(dv/dt) KCL The Attempt at a Solution At t<0 I found Vc to be 8 volts which should be correct...
  48. T

    Engineering Induction Motor Problem, How to find Rc

    Homework Statement A three phase 220 V , 60 Hz, six poles 10 hp induction motor has the following circuit. Parameters on a per basis referred to the stator: Rs = 0.334 Ω, R’R = 0.147 Ω, Xs = 0.498 Ω X’R = 0.224 Ω , Xm = 12.6 Ω The rotational losses including the core losses amount to 262 W...
  49. goonking

    Engineering RC circuit with current source

    Homework Statement Homework EquationsThe Attempt at a Solution so when t=0, the capacitor is a closed circuit. The Req of the circuit is (20k)(30k)/(20k+30k)= 12000 ohms. U = I Req = (7.5x10-3A) (12000 ohms) = 90 Volts so there is a voltage drop of 90 volts across the 20k resistor (R1)...
  50. R

    2nd order RC filter with two equal poles

    Is it possible to make a 2nd order CR LPF or HPF where the cut off frequencies for each pole are equal? Here is a calculator for this system which includes the transfer function.http://sim.okawa-denshi.jp/en/CRCRkeisan.htm I figured that I need to try to solve the denominator of the transfer...
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