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. H

    Solve RC Circuit Problem: Calculate Charge on Capacitor

    Homework Statement What is the charge on the capacitor? Homework Equations Kirchoff's rule change in V =q/c The Attempt at a Solution I want to use Kirchoff rule but I don't know if this is the right way to go.
  2. R

    Charging Time for RC Circuit with Capacitor and Resistor

    Homework Statement A 1234. pF capacitor and a 5.6 × 106 ohm resistor are connected in series to 78. volts EMF. Approximately how long does it take the capacitor to become almost fully charged? Homework Equations Vf=Vo(1-e^(-t/RC)) The Attempt at a Solution I'm not sure if the...
  3. C

    RC Circuit - Post-Lab Questions

    Homework Statement What is the voltage across a capacitor after a time of two constants when charging from zero voltage. When discharging from a fully charged condition? Homework Equations VCapacitor = VBattery(1 - e-t/2T) VCapacitor = VMaximum * e-t/2T The Attempt at a Solution I'm...
  4. H

    Reducing Energy in an RC Capacitor: Solving for Discharge Time

    Homework Statement At what time (in ms) after the discharge begins is the energy stored in the capacitor reduced to half its initial value? RC=7 ms Homework Equations RC=7ms E=.5CV^2 E=.5Q^2/C E=.5QV Q_f = Q_i * e^(-t/RC) The Attempt at a Solution I don't even know where to go...
  5. RAHIL008

    Solving RC Car Motor Problem - Get Expert Help

    hi, I have a RC car that uses 27mhz radio frequency and 8v power supply. The motor(6v,possibly)that rotates the wheels runs with interruptions,i have tried adding two new 0.1Microfarad capacitors(ceramic)in the same way as they were from the manufacturer, bit it didnt help,maybe the polarity...
  6. K

    What is the current in each resistor in a complex RC circuit?

    Homework Statement Find the current I1 in the 1.2 resistor at the bottom of the circuit between the two power supplies. Answer in units of A. 015 (part 2 of 3) 10.0 points Determine I2. Answer in units of A. 016 (part 3 of 3) 10.0 points Determine I3. Answer in units of A...
  7. C

    Solving a Basic RC Circuit: Charge on Capacitor from 537 to 195 μC

    Homework Statement The capacitor in the circuit has 537 μC of charge on it at t=0. The resistor is 1,923 Ohms, and the capacitor is 1,251 microFarads How long will it take for the charge on the capacitor to drop to 195 μC? Please use only SI (metric) system units in your answer...
  8. S

    RC car electric start simple circuit

    I'm a communications electrician in the Navy. I went through some electronics theory about eight years ago. Now, I'm trying to build a simple circuit for an on-board electric starting system. The vehicle runs on a small Nitro Methane motor and uses a glow plug for the ignition. I'm using a...
  9. J

    Calculating Energy in an RC Circuit

    Homework Statement I have an RC Circuit. There's the EMF (voltage supplier; battery), a resistor, and a capacitor. They are all in series. I need to prove that --the energy stored in the capacitor through it charging equals 1/2 the energy supplied by the EMF Then I need to show --how much...
  10. F

    Engineering Solving RC Circuits with Switch: Finding Vs(t) and Vc(t)

    Homework Statement i need to find the Vs(t) and Vc(t) http://img32.imageshack.us/img32/9071/circuiten.jpg The Attempt at a Solution since there is a switch i used two cases to find the Vc one with switch on and switch off switch on...
  11. L

    RC circuit - charge on capacitor after a long time

    RC circuit - charge on capacitor after a "long time" Circuit: 10V goes to 100ohm resistor, then there's a branch point. One side leads to a a resistor R2 = 100ohms and the other to a capacitor with C = 1uF. The switch is located just before R1, and is closed for a "long time." Solution: Ok...
  12. N

    RC Charge/Discharge for Electrochemical Capacitor

    I am a student working on designing an electrochemical capacitor (an area which i have limited experience). When I charge this capacitor through an RC circuit I notice two non ideal effects. I need to adress the cause of these effects if I can ever hope to correct them. The first problem is...
  13. C

    Calculating Voltage Across R1 in an RC Circuit with a Capacitor

    In the following circuit R1 = 12.9 Ohms, R2 = 3 Ohms, V = 39 Volts, and C = 10.1 micro-Farads. If one waits 2 time constants after the battery has been connected (charge in capacitor is zero before the battery is connected), what is the voltage across R1 in volts? Hint: first find the charge...
  14. E

    Potential across a capacitor in an RC circuit

    Homework Statement http://img14.imageshack.us/img14/4822/2116b.png The circuit has been connected as shown in the figure for a “long” time. What is the magnitude of the electric potential across the capacitor? Answer in units of V. Homework Equations Kirchoff's rules V = IR V(t) =...
  15. 0

    Integration and RC Step response

    Integration Homework Statement Hi everyone, I'm new here. This is my first post. I found physicsforums when researching on google a solution for a doubt I've had when trying to solve rc step response. Basically, the RC analyse showed at...
  16. Q

    Solving RC Circuit Equation with Internal Resistance

    Homework Statement ok erm, i know how to get the equation V = EMF (1 - e^(-t/RC)) in a RC circuit but what if i had to take into account the internal resistance r of the voltmeter measuring the voltage across the capacitor? meaning now, the circuit contains a resistor R in series with, an...
  17. M

    RC Circuit find capacitor charge

    Homework Statement The capacitor in an RC circuit (R = 130 \Omega, C = 40uF) is initially uncharged. 1) Find the charge on the capacitor in the circuit one time constant (tau = RC) after the circuit is connected to a 9.0- V battery. 2) Find the current in the circuit one time constant (\tau...
  18. F

    Engineering RC Circuit Rise Time: 1k-1000k | V=5V | C=0.01uF

    Homework Statement Calculate the rise time (the time require for the output to go from 10% to 90% of its final, or steady state, value) for the circuit shown above when a step input of 5V is applied for the following resistor values: 1k, 10k, 100k, 1000k with C equal to 0.01uF...
  19. W

    Solving for t in an RC Circuit

    Homework Statement The capacitor in an circuit is initially uncharged In terms of R and C, determine the time required for the charge on the capacitor to rise to 50% of its final value. In terms of R and C, determine the time required for the initial current to drop to 10% of its...
  20. T

    RC time constant lab, Current vs time

    Homework Statement In my lab we where given a simple circuit and told to get some data of a capacitor charging and discharging. Thus I now have a graph of current vs time, we used semi-log paper for this so the graph would be a straight line. We are given the value of the resistor and...
  21. O

    Small wheel folding bike, which rc engine best for lightweight n performance ?

    I got a small 16inch folding bike weight 13kgs and managed to shed it down to 9kg and working in weight reduction further... eg using hollow shaft at the peddle and using clips at the axles and replacing to 14inch rims and redoing the frame in lighter stainless 201 - these are my next to-do...
  22. A

    Self sustaining (DC) RC circuit

    hi i want to drive led's through a RC series (time constant) circuit, which is powered by a DC source and when the capacitor is fully charged,, the switches should be such that the capacitor will discharge automatically glowing the led's from opposite direction, So the led's will give one...
  23. P

    Designing a Computer Simulation for Genetic Optimization of RC Aircraft

    Hello, My project is to design a new type of flying RC toy, and since i am not an engineer and I don't know aerodynanic well, I am trying to craft some kind of aerodynamic simulator on my computer, then run some genetic programming to design from scratch any kind of small aircraft capable to...
  24. R

    Capacitor RC Value - Charging/Discharging Explained

    Dear Experts, I charged a capacitor that is in series with a resistor using a DC power source. In practice, does a capacitor charge/discharge as per the calculated RC based on formula? For example, does the capacitor really fully charge / discharge at 5RC? Sincerely Ramone
  25. U

    How Can I Ensure Each IR LED Activates Only Its Corresponding Phototransistor?

    RC stands for remote control, but where in the situation I have no radio transmitter, it was only reasonable that I had better used IR LEDs and phototransistors for the receivers. I'm only 12, have a restricted budget of no more than $30, and less time on hand. In fact, school resumes on the...
  26. T

    Need help modifying rc car circuit

    Hello, I have this old toy RC car and a pager and I am wondering if a small hack, using the two is possible or not. The pager doesn't work but its motor does. I want to make a new "pager" that vibrates when the car's remote is used. The car has a small reciever circuit (27MHz if that's of any...
  27. S

    RC and RL(frequency and potential difference)

    Homework Statement 1.(RC in AC)What will happen to the potential difference on the capacitor as the frequency increases? In terms of the reactance of the capacitor, why might this happen? 2.(RL in AC) What will happen to the potential difference on the inductor as the frequency increases...
  28. J

    Engineering Transfer function of RC circuit

    Hello all, I need transfer function of this circuit (it is Bandaxall tone stack). Here is the sheme: Any help would be greatly appreciated.
  29. B

    DE explaining simple RC circuit

    I'm trying to wrap me head around what should be a very simple system, but I just can't manage it. I know there is no closed form for this problem (ignoring a voltage step like is shown in the diagram below, imagine it is a arbitrary voltage supply, or even more exactly, that R2 changes over...
  30. N

    Simple way to amplify voltage to RC helicopter tail rotor?

    My brother bought a http://www.centrix-intl.com/details.asp?productid=4909" RC helicopter. It has a tail rotor which is mounted parallel with the ground and enables the chopper to go forwards or backwards. The helicopter goes backwards great, but it doesn't go forward too well. I would like to...
  31. A

    Engineering Solve RC Op-Amp Circuit Connected in a Non-Inverting configuration

    How would you solve an RC op-amp circuit connected in a non-inverting fashion, such that the second resistor is replaced by a capacitor. This is not the usual differentiator or integrator circuit as far as I can tell? No specific problem, just generally speaking, how would you approach this
  32. O

    How Do You Calculate the Oscillation Period and Energy Gain in an LC Circuit?

    Homework Statement An oscillating LC circuit has a current amplitude of 7.20 mA, a potential amplitude of 250 mV, and a capacitance of 240 nF. (a) What is the period of oscillation? (e) What is the maximum rate at which the inductor gains energy? Homework Equations Possibly: Energy stored in...
  33. J

    RC Circuit discharge question -

    RC Circuit discharge question - test prep for tomorrow Homework Statement A charged 6\muF capacitor is discharged across a 2\Omega resistor. How long does it take to lose half its stored energy? Homework Equations ...so many: Q = CV V = IR W = I2R U = 1/2 QV V = V0e-t/RC The...
  34. M

    Engineering How does the current through an inductor affect the RC circuit?

    This is for question 7.53b) . I understand that the inductor acts like a short circuit but how is the current through the inductor affected? Wont the current source (6 A) split at the node before the 4 ohm resistor and before going into the 2 ohm resistor? Also to get the Equivalent Resistor...
  35. H

    Is Bulb B the Brightest When the Capacitor Has Half its Maximum Charge?

    SOLVED - RC Circuit - Question http://img291.imageshack.us/img291/5585/bulbd.th.jpg This problem is giving me a headache. I feel certain that bulb B is the brightest when the capacitor has half its maximum charge. However, I am having a hard time coming up with equations for the circuit...
  36. R

    E&M lab(Finding the capacitance in an RC circuit from the time constant)

    Homework Statement sigh* Well, I have more than a week to do this lab, and usually I don't resort for help here, but on this lab there are so many things I am unsure of. So here's the setup of the lab: I have a one Farad capacitor, a DC power supply, a multimeter, a bunch of...
  37. C

    Calculating Potential Difference on A Capacitor, RC Circuits

    The circuit of Figure P.72 has been turned on for a long time, so that you can ignore the transient behavior of the capacitor. Voltage of Battery V = 31 V (e) What is the potential difference across the capacitor C (C = 9 µF)? I thought about using Kirchoff Voltage Law, but I also though that...
  38. L

    Building an rc chopper and have a question to do with damping vibrarions

    I have already built most of the chopper but am trying to add an accelerometer. Let's say the blade is rotating at 600rpm, this is causing vibrations throughout the vehicle at 10hz. I want to make a compartment which doesn't feel most of these vibrations. I'm thinking of building something using...
  39. K

    Building and designing a rc plane frm scratch

    heyy guys i am participating in an aero competition in which the problem stmt is to design an acrobatic hand launched rc plane of wingspan 3 ft max which can perform stunts like a vertical loop, sharp turns and 360 roll...can you please tell me how to begin designing this aircraft...i...
  40. S

    How Does Current Flow in a Charging RC Circuit?

    Homework Statement In an RC circuit under charging, does the current actually flow across the plates of a parallel plate capacitor? Does charge emanate from both terminals of the battery and move to the plates of a capacitor or does charge only emanate from positive terminal and get...
  41. F

    Rewiring an RC car. (56k warning)

    I'm trying to rewire my RC car. Basically, the car has two states that are important. State 1: The Car is on. Light 1 (the underglow) is on. Light(s) 2 (The Headlights and Brakelights, which I believe are, for all intents and purposes are the same) is off. State 2: The Car is on and a...
  42. C

    Can someone explain this rc circuit prob

    For a long period of time the switch S is in position “b”. At t = 0 s, the switch S is moved from position “b” to position “a”. ....3 M ohm l---------------^^^^^^-----------------l l........…......l l...1 M ohm...4micro F.....l b l---^^^^^^^^^-------------ll---------/ i...
  43. T

    How Does Switching Affect Bulb Brightness in an RC Circuit?

    Three common light bulbs and two identical capacitors are connected to a battery as shown in the figure below. The switch has been open for a long time. At t = 0 the switch is closed. The light bulbs are all identical and the battery has a value V = 6 V. (The brightness of a light bulb depends...
  44. 6

    How to calculate time constant tau for RL and RC circuits from their graph?

    I made graphs of simple RC and RL circuits. We were told to mark off at 10% of the rise and 10% away from the max. This gives a delta. We were then supposed to use this information form the graph to calculate tau, and compare it with the theoretical value. I know how to calculate the...
  45. C

    Step and Impulse Responses in RC Circuits

    Hello very body i got confused understanding how we can get the derivative of V(t) equal to Hv(t) : V= (1/R) e^(-t/RC) U(t) its derivative V' = Hv(t) = -(1/R²C)e^(-T/RC) U(t) +(1/R)&(t) where : U(t) is the unite step fonction and &(t) is the delta fonction please some help thanks for...
  46. C

    How Is Current Derived in a Series RC Circuit with an AC Source?

    can anyone show me the derivation of an expression for current in a series RC circuit with an AC source? I have seen many for DC sources simply using KVL is it the same for AC? I would imagine that a two part solution is required: 1) homogeneous solution 2)using undetermined coefficients as...
  47. I

    What's the best/strongest material for RC car models?

    I like to play and abuse RC car models like this: However, when making big jumps or high-speed crashes (they can even reach 90mph), even steel parts gets damaged and needs to be substituted. See these damaged/broken parts for example: http://img169.imageshack.us/img169/4286/cimg1700.jpg...
  48. S

    How do switches and resistors affect a RC circuit's charge and energy output?

    Homework Statement Consider the electrical circuit consisting of an E = 6 V battery, two switches S1 and S2, two resistors R1 = 4 ohm and R2 = 2 ohm, and a capacitor C = 2 \muF. The internal resistance of the battery may be ignored. Initially the switches are both open and the capacitor has no...
  49. R

    How Does Capacitor Configuration Affect the RC Circuit Time Constant?

    Homework Statement Three identical capacitors are connected with a resistor in two different ways. When they are connected as in part A of the drawing, the time constant to charge up this circuit is .34s. What is the time constant when they are connected with the same resistor as in part B...
  50. P

    A bit lost on the RC circuit differential equation

    Homework Statement Solve the differential equation R\frac{dq}{dt} + \frac{q}{C} = v_0 R is resistance, q is charge, t is time, C is capacitance, and v_0 is the EMF of the power supply.Homework Equations First-order linear differential equation solving method The Attempt at a Solution This is a...
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