[Prev][Next][Index][Thread]
Re: 50%
At 06:20 AM 11/12/96 +0000, you wrote:
>From ed-at-alumni.caltech.eduMon Nov 11 23:17:44 1996
>Date: Mon, 11 Nov 1996 19:51:15 -0800 (PST)
>From: "Edward V. Phillips" <ed-at-alumni.caltech.edu>
>To: tesla-at-pupman-dot-com
>Subject: Re: 50%
>
>"Total energy in caps
>Joules = 1/2C(V/2)^2 + 1/2C(V/2)^2 = 1/2(1)(V/2)^2 + 1/2(1)(V/2)^2
>Joules = 1/2(1)(V^2/4) + 1/2(1)(V^2/4) = V^2/8 + V^2/8 = 200/8 = 25 total
>joules in the caps.
>Energy is conserved
>
>Coulombs in first cap = CV = (1)(10) 10 coulombs
>Total coulombs in caps = 2CV = 2(1)(5) = 10 coulombs
>Coulombs are conserved
>
>Does anyone know how to find what the voltage would be if the second
>capacitor was 1/2 farad instead of 1 farad? The voltage would be greater
>than V/2."
>Answer:
>1 farad capacitor charged to 10 volts = 1*10 = 10 coulombs
>1 farad capacitor connected to 0.5 farad capacitor = 1.5 farads
>Final charge = 10 coulombs
>Final voltage =10 coulombs/1.5 farads = 6.66666666 volts
>Final energy = 0.5*1.5*(6.66666666)^2 = 33.333333 joules
>compared to 25 joules for the two capacitor case.
> This result is reasonable. In the limit, when an
>infinitessimally (sp?) small capacitor is connected across
>a large one there is no change in voltage or energy.
>Ed Phillips
>
----------------------------------------
Ed -
Congratulations. Your answer and reasoning are correct but I have had people
tell me that with a total of less capacity the answer should be less not
more energy. Connecting and reconnecting capacitors can be tricky calc
problems. It gets me into trouble sometimes.
It can be confusing when applying the above to Tesla coils. We are saying
that a smaller toroid will have more energy and should give more spark. Of
coarse, this isn't correct because tests indicate otherwise. The reason is
the problem is different. The toroid capacitor is being continually fed
energy. This is one reason the spark is shorter when only one shot is used,
the energy is limited.
Jack C.