Lost Energy (was Re: Van de Graaff /Pelletron) (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 20 Jan 2004 07:39:26 +1300
From: Malcolm Watts <m.j.watts@xxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Lost Energy (was Re: Van de Graaff /Pelletron)

Hi Ed,
      This is an old one, the answer to which also answers Alfred's
last question on this topic:

On 19 Jan 2004, at 10:59, High Voltage list wrote:

<snip>

>  Here's another question whose answer should be obvious, but has
>  puzzled
> lots of guys.  Suppose we take a capacitor charged to voltage V and
> connect it to an identical one with no charge.  The original energy
> was 1/2 CV^2.  Now we have two capacitors with voltage V/2, and each
> has an energy of 1/2 C(V/2)^2; the sum is CV^2/4, or half the starting
> energy. Question is "Where did the LOST energy go?".
>
> Ed

A part of the puzzle is missing - it is usually stated that no
resistance is present.

     When the capacitors are connected, a current flows. That being
so, an inductive element is also present by proxy. Hence an LC
circuit is formed. In fact, one gets an oscillation which dies as
radiation occurs and this also means that a resistive component is
present.

Malcolm