       Re: capacitor equation solution not working

• To: mathgroup at smc.vnet.net
• Subject: [mg119790] Re: capacitor equation solution not working
• From: Dana DeLouis <dana.del at gmail.com>
• Date: Wed, 22 Jun 2011 07:06:05 -0400 (EDT)

```... I[t_]:= If[t<10||t>60,0,1]

Hi.  Just 2 cents for an alternative.
For a signal pulse, sometimes I'll remember it as follows:

What we have...
If[t<10||t>60,0,1];

FourierTransform[%,t,w]
(E^(35 I w) Sqrt[2/\[Pi]] Sin[25 w])/w

InverseFourierTransform[%,w,t]
1/2 (Sign[60-t]+Sign[-10+t])

Plot[%,{t,0,100}]

Or transformed into something like this:

f[t_]:=UnitStep[t-10]-UnitStep[t-60]
f[t_]:=UnitStep[-(t-10) (t-60)]

= = = = = = = = = =
HTH  : >)
Dana DeLouis

On Jun 17, 12:09 am, "J and B" <noslow... 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
>
> My code.
> I[t_]:= If[t<10||t>60,0,1]
> Plot[i[t],{t,0,100}]
> Eq=v'[t]==i[t]/c
> c=1;
> Soleq==v[t]/.NDSolve[{eq,v==0},v[t],{t,0,100}],[]
> Plot[soleq,{t,0,100}]

```

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