       Re: capacitor equation solution not working

• To: mathgroup at smc.vnet.net
• Subject: [mg119694] Re: capacitor equation solution not working
• From: michael partensky <partensky at gmail.com>
• Date: Fri, 17 Jun 2011 05:51:53 -0400 (EDT)
• References: <201106170409.AAA28826@smc.vnet.net>

```>
> On Fri, Jun 17, 2011 at 12:09 AM, J and B <noslowski at comcast.net> wrote:
>
>> I am trying to solve a very simple circuit, one that has only a capacitor
>> in
>> it.  What am I doing wrong?  The final graph should show that the
>> capacitor
>> has discharged, but its staying constant.  I have current starting at t=10
>> and ending at t=60.
>> I hope I have used the correct way to put in my code, I am using a new
>> computer and I having trouble with my email program.  Any advice would be
>> appreciated.
>>
>> Thanks
>>
>> I did not check the rest , but fixing two formatting errors can
> >
> > My code.
> > I[t_]:= If[t<10||t>60,0,1]
> > Plot[i[t],{t,0,100}]  (* you use different letters for the current, iand
> I; btw, I is reserved for the imaginary unit *)
>
> *Eq*=v'[t]==i[t]/c
> c=1;
> >
> > c=1;
> > Soleq==v[t]/.NDSolve[{*eq*,v==0},v[t],{t,0,100}],[]
> > Plot[soleq,{t,0,100}]
> ( **Eq* and *eq* are also different *)

Btw, your circuit without a resistor is "short": the capacitor will
discharge instantly.
Be also aware that the derivative of a step function is expressed though the
so called delta-function which must be handled with extreme care.

Best
MP

```

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