       Re: Mathematica and RC circuits

• To: mathgroup at smc.vnet.net
• Subject: [mg56919] Re: Mathematica and RC circuits
• From: dh <dh at metrohm.ch>
• Date: Tue, 10 May 2005 03:42:22 -0400 (EDT)
• References: <d5hu1r\$jtc\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Hi,
your "question" is not exactly very clear, but I try my best. If you
want a good answer, you should put some effort into putting a good
question. See below
Sincerely, Daniel

1s1kjake wrote:
> I am trying to use Mathematica 5.1.1 to solve an RC circuit, and I am
> having problems. When ever I use I or i for the current the program
> keeps running untill it close down.
I is used as the imaginary unit and can not be used as a variable name.
As for i, there is no problem using it as a variable name.
Then other problem, how do I set
> up Mathematica to solve this equation for dvdt,  i = v/r + c dv/dr.

Guessing from your equation I think you have a parallel circuit of an
resitor and a capacitor. But then the term dv/dr should read dv/dt. A
sensible question is to ask for the voltage, given the current. As you
have a first order DG you also need a starting value, say v==0.
Well, this gives the following equations:
eq={i[t]==v[t]/r+c v'[t], v==0};

Lets make an example by choosing:

i[t_]=1; r=1; c=1;

this is solved for the time {0,1} by:

sol= v/. NDSolve[eq,v,{t,0,1}][];

and plotted:

Plot[sol[xt],{t,0,1}]

> Then I want to plot this equation based on diferent current imputs.
> thanks
>

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