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. Juanda

    Auto/Motor Design to 3D print RC car - Steering

    I am planning to design an RC car to 3D print it and have some fun. It will mostly be a learning experience with the by-product of having a hopefully fun RC car by the end of it. That will probably force some decisions that might be overengineered and negatively impact performance but building...
  2. J

    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...
  3. 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?
  4. PhysicsTest

    Simple RC Hardware Circuit Understanding -- Questions

    I need to understand the below hardware circuit I am not sure about the type of the signals at signal1 and signal2, i have assumed DC signals initially. Then when i simulated in LT spice, the signal at Output is +5V. But if i assume the signals at signal1 and signal2 as Sine wave, then C1 and...
  5. S

    VTOL RC Airplane Tricopter COG, Liftoff Weight Calculations

    Hello, I am interested in making an RC plane as illustrated. Some questions: 1. Given that the build material of the plane will be 3d printed out of PLA and I want the wingspan to be between 1.2m - 1.35m ideally. How can I calculate the minimum wingspan/wing shape/wing area to carry a payload...
  6. miyelmunshi

    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. N

    What is necessary for a hypothetical supersonic speed Radio Controlled Jet?

    Hi everyone! :) While i watched rc jet exhibitions on youtube, i find that the most fast of this RC reached +700 Km/h. When i browse more information about the tourbine, i realized that for a hypothetical supersonic RC the mechanical system of the tourbine must have a complete air compressor...
  8. C

    Purely passive RC Phase Shift Oscillator?

    It is possible to build a purely passive RC phase shift oscillator with 2 separate (in the future) RC stages like this? Where there would be 2 RC networks that each provide 180 degrees of phase shift. Of course, there would be a buffer in between the 2 RC networks so that they behave as 2...
  9. C

    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...
  10. I

    Calculating Current in a Series RC Circuit

    Hi , i was just wondering how would i find the current through a capacitor (Series RC circuit) I found a questions online which asks to find the voltage and the current through a capacitor at 1kHz and 10Khz Capacitor = 0.01uF Resistor = 100 Ohms Voltage Source = 10v ive done some...
  11. J

    B RC Low Pass Circuit Sine Wave Response

    Hey Everyone, I am trying to gain a level of fundamental understanding of an RC circuit sine wave response through the mathematics and was wondering if someone could help me work it out. Fundamentally a sine wave is represented by the equation y=-ky'' . When a sine wave is used as the input...
  12. brainbaby

    LT spice result analysis, Capacitance Multiplier vs RC filter circuit

    Hi friends, I have simulated two circuits, one is an RC filter and other is a Capacitance multiplier. My aim of experiment is to validate a decrease in Iout (load current) of CM circuit as compared to load current in RC filter circuit. Theoretically, Iout (CM circuit) < Iout (RC filter) Vp-p...
  13. J

    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?
  14. X

    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...
  15. Kaguro

    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}##...
  16. greg_rack

    B Difference between RC and RRC circuits

    Circuit A(RC) Circuit B(RRC) Hi guys, the thing I don't get is why the maximum charge of the A capacitor is ##q_{0}=C\cdot EMF## whilst in the other case you must consider the drop in tension caused by the first resistor, so the maximum charge of the cap is ##q_{0}=C\cdot (EMF-V_{R1})##. Aren't...
  17. greg_rack

    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...
  18. greg_rack

    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...
  19. jozefmak

    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...
  20. D

    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...
  21. cnh1995

    Engineering AC transient 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?
  22. hmzi123

    Engineering Solve RC Integrator Circuit Problem | Romania Student

    Hello, i am student from Romania ( first year) and my physics teacher told us to solve this problem. We know that C=150 nanofarad, R= 1000 ohms, and the frequency we should take is more then 1061 ( 10kHz, to be more exactly). My problem is that i don't know what to take as V1 ( i took it coswt...
  23. 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...
  24. okandrea

    Structural Systems: Steel and Reinforced Concrete (RC)

    I've been looking over precedents for a design project and I noticed that the most commonly used systems are either steel or reinforced concrete structural systems. Is it possible for a steel structural system to be connected to a reinforced concrete structural system? If so, how does it work...
  25. K

    Discharging this capacitor in an RC bridge circuit

    The voltage source in the circuit below has been switched on for a long time when the switch S switches off. How long will it take before the current coming out of the capacitor has become less than 1 mA? My attempt: I am far from sure that my solution is correct. This is because i...
  26. eyespy

    A circuit with switches, capacitators and resistors

    To solve this question first I calculated the potential energy the capacitor A stored. It's equal a: Ca.V²/2. Ok, so when switch S1 is open and S2 is closed I calculated the equivalent capacitance as if they were in series --> 1/Ceq = 1/Ca + 1/Cb --> Ceq = (Ca.Cb)/(Ca+Cb). So I used the formula...
  27. M

    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...
  28. mastermechanic

    Cost of a 50 km range RC system & Type of Antenna

    Hello everyone, I'm a mechanical engineering student working on a reconnaissance/surveillance UAV system. To summarize it, 1-) It will either have FLIR camera system (If I can afford it) or GoPro with turret system. In either case it will transmit 4K or lower quality video record. It will also...
  29. 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...
  30. L

    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...
  31. J

    Oscillator Frequency of a Ring Oscillator with RC feedback

    I'm not sure how will this oscillator work. Assume A is low, so B will be high and the capacitor will charge through B-C- 2Mohm. Now even D has gone high, so A will be high and B will be low and C will discharge. I'm not sure how the voltage divider rule across RC will take into effect. I found...
  32. Simpcar

    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...
  33. Z

    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...
  34. C

    I RC charging - intuition behind equal dissipated energies?

    Assume that a resistor R charges a capacitor C, whose other terminal is connected to the ground. The charge at time t = 0 is assumed to be null and the supply voltage is equal to V. We have, as is well known, ##i = \frac{V}{R} e^{-\frac{t}{RC}}##. Integrating ##\frac{i^2}{R}## between t = 0 and...
  35. Abo

    RC time constant problem — confusing problem statement

    Hello! It says that the Time Constant of an RC circuit is equal to 100 ms. What is the energy that remains in the circuit after 300 ms? "Nothing mentioned about whether it is in falling or rising edge". The formulas that I have been using are : W = 0,5 (C* V^2) V = V0 ( e^-t/rc ) since I don't...
  36. Abdullah Almosalami

    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...
  37. S

    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...
  38. Eduardo Leon

    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...
  39. Shivang kohlii

    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...
  40. FreeForAll

    Driving an RC car in a vertical loop, What formula to use?

    I once drove my RC car in a vertical loop in a concrete drain pipe. If you know the diameter of the pipe, and the weight of the vehicle, what is the formula used to determine the minimum speed required for it to complete the loop?
  41. bornofflame

    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...
  42. bornofflame

    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...
  43. R

    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...
  44. 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...
  45. Y

    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...
  46. Ruskointhehizzy

    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...
  47. D

    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...
  48. C

    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...
  49. T

    How accurate is my wind tunnel for testing RC plane wings?

    Hi everyone, I am new and I hope I'm putting this in the right section. I am currently a Sophomore in High school and I am building a wind tunnel. It's not for a class but rather its is like an independent study. I have been into planes pretty much all my life and I am hoping to get a pilots...