Re: capacitor equation solution not working

• To: mathgroup at smc.vnet.net
• Subject: [mg119695] Re: capacitor equation solution not working
• From: michael partensky <partensky at gmail.com>
• Date: Fri, 17 Jun 2011 05:52:04 -0400 (EDT)
• References: <201106170409.AAA28826@smc.vnet.net>

```Sorry, my last comment is irrelevant for your setting where the current is a
given function (which is unusual but formally valid).
Best
MP

On Thu, Jun 16, 2011 at 11:49 PM, michael partensky <partensky at gmail.com>wrote:

>
>> 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]==0},v[t],{t,0,100}],[[1]]
>> > 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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