Xref: utzoo sci.electronics:6394 sci.physics:8389
Path: utzoo!attcan!uunet!lll-winken!ames!pacbell!pbhya!whh
From: whh@PacBell.COM (Wilson Heydt)
Newsgroups: sci.electronics,sci.physics
Subject: Re: HV Cap Fun!
Summary: Hidden assumptions
Message-ID: <27119@pbhya.PacBell.COM>
Date: 1 Jun 89 22:15:56 GMT
References: <4924@m2c.M2C.ORG> <3806@mit-amt> <20772@quacky.mips.COM>
Followup-To: sci.physics
Organization: Pacific * Bell, Oakland, CA
Lines: 28

In article <20772@quacky.mips.COM>, vaso@mips.COM (Vaso Bovan) writes:
> A Paradox of Capacitor Energy Storage
> 
> I've heard several competing answers to this paradox. None is entirely
> satisfactory:
> 
> Consider an ideal 2uF (for computational ease) capacitor charged by a 10 volt 
> source. Eventually, the energy stored is (1/2)*CV^2=100 joules.

Please--if you want to store 100 joules, use a 2 F capacitor.

> Consider the capacitor to be isolated from the voltage source, and then
> directly shorted across an identical (ideal) capacitor. Eventually, the
> voltage across each capacitor will be 5V. Now, there are two equally
> charged capacitors, each storing (1/2)*CV^2= 25 joules, for a total of
> of 50 joules.  What happened to the other 50 joules ?

Why do assume the result will be 5 v.?  (Have you actually done
the experiment?)  Aren't you more likely to have 2 caps at 10 * (2 ** -2) v.?
Each storing 50 joules?  (Or 50 microjoules for your 2  uF units.)

    --Hal

=========================================================================
  Hal Heydt                             | In the old days, we had wooden
  Analyst, Pacific*Bell                 | ships sailed by iron men.  Now
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