Re: RC circuit

*To*: mathgroup at smc.vnet.net*Subject*: [mg56845] Re: [mg56844] RC circuit*From*: "David Park" <djmp at earthlink.net>*Date*: Sat, 7 May 2005 15:35:07 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Here is one method to solve your exercise. You can use 'i' for current but not 'I', which is a reserved symbol. In general you should avoid symbols that start with capital letters. Also notice that 'equal' is represented by == in Mathematica. Here is your equation. Clear[v]; deqn = i == v[t]/r + c v'[t]; Now we solve the equation and add the initial condition that v starts at 0 when t == 0. Clear[v]; dsolutions = DSolve[{deqn, v[0] == 0}, v, t] v[t_] = v[t] /. Part[dsolutions, 1, 1] {{v -> Function[{t}, ((-1 + E^(t/(c*r)))*i*r)/E^(t/(c*r))]}} ((-1 + E^(t/(c*r)))*i*r)/E^(t/(c*r)) Now we need a set of data for some particular case to plot. (data = {c -> 3, i -> 2, r -> 2.5}) // TableForm Now we can plot, We want to substitute the data into the expression for v[t] and we want to evaluate the expression in the Plot statement. I've added labels and text to make a more informative plot. Plot[Evaluate[v[t] /. data], {t, 0, 50}, Frame -> True, FrameLabel -> {"t seconds", "v volts"}, PlotLabel -> "Voltage in an RC Circuit", Epilog -> {Text["c = 3 Farads", {30, 4}, {-1, 0}], Text["i = 2 Amperes", {30, 3.5}, {-1, 0}], Text["r = 2.5 Ohms", {30, 3.0}, {-1, 0}]}, ImageSize -> 450]; It does take a little time to learn the syntax and available commands in Mathematica before one can efficiently use it to solve practical problems and homework exercises. But it is worth it if you expect to do much of it. David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: pennsylvaniajake at netscape.net To: mathgroup at smc.vnet.net [mailto:pennsylvaniajake at netscape.net] Two ?'s I am trying to solve a simple RC circuit. ?1 I can's use the letter "i" for current, is there a way around this ? ?2. How do I solve this equation for dv/dt, eq: i = v/r + C dv/dt thanks >

**Follow-Ups**:**Re: Re: RC circuit***From:*DrBob <drbob@bigfoot.com>