Return-Path: Received: (qmail 16015 invoked from network); 8 Nov 2002 12:50:27 -0000 Received: from warrior.services.quay.plus.net (212.159.14.227) by mailstore with SMTP; 8 Nov 2002 12:50:27 -0000 Content-Transfer-Encoding: 8bit Received: (qmail 12337 invoked from network); 8 Nov 2002 12:06:19 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from post.thorcom.com (193.82.116.70) by warrior.services.quay.plus.net with SMTP; 8 Nov 2002 12:06:19 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 4.10) id 18A7pM-0003cw-00 for rsgb_lf_group-outgoing@blacksheep.org; Fri, 08 Nov 2002 12:01:32 +0000 Received: from [147.197.200.9] (helo=hestia.herts.ac.uk) by post.thorcom.com with esmtp (Exim 4.10) id 18A7pL-0003cn-00 for rsgb_lf_group@blacksheep.org; Fri, 08 Nov 2002 12:01:31 +0000 Received: from gemini ([147.197.200.44] helo=gemini.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 18A7jg-000706-00 for rsgb_lf_group@blacksheep.org; Fri, 08 Nov 2002 11:55:40 +0000 Received: from [147.197.232.252] (helo=rsch-15.herts.ac.uk) by gemini.herts.ac.uk with esmtp (Exim 3.33 #1) id 18A7je-0003qD-00 for rsgb_lf_group@blacksheep.org; Fri, 08 Nov 2002 11:55:39 +0000 Message-ID: <5.1.0.14.0.20021108112020.00aeef28@gemini.herts.ac.uk> X-Sender: mj9ar@gemini.herts.ac.uk X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Fri, 08 Nov 2002 11:51:38 +0000 To: rsgb_lf_group@blacksheep.org From: "James Moritz" In-reply-to: <7D653C9C42F5D411A27C00508BF8803DCB9CBB@mail.dstl.gov.uk> MIME-Version: 1.0 X-MailScanner: No Virus detected Subject: Re: LF: To Ponder over the weekend Content-Type: text/plain; charset=us-ascii; format=flowed X-Spam-Status: No, hits=0.1 required=5.0tests=DEAR_SOMEBODY,IN_REP_TO,SPAM_PHRASE_00_01version=2.42 Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Dear Andy, LF group, At 09:38 08/11/2002 +0000, you wrote: >This simple puzzle caused more discussion in my office this morning than it >had any right to.... Here is another conundrum along similar lines - you have two identical, loss-free 1uF capacitors, one is charged to 10V, the other is discharged. You then connect the two in parallel so the total C is now 2uF - charge will flow from the charged capacitor into the discharged capacitor. Assuming charge Q is conserved, and that Q=CV, the voltage must now be 5V. But the stored energy in a capacitor =1/2CV^2, so with the single charged capacitor, the stored energy is 1/2 x 1u x 100 = 50uJ, while with both capacitors in parallel it is only 1/2 x 2u x 25 = 25uJ. So where has the other 25uJ gone? Cheers, Jim Moritz 73 de M0BMU