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From: greg@jif.berkeley.edu (Greg)
Newsgroups: sci.physics,sci.electronics
Subject: Re: capacitors
Message-ID: <10227@agate.BERKELEY.EDU>
Date: 23 May 88 17:09:42 GMT
References: <2992@phoenix.Princeton.EDU>
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Reply-To: greg@bosco.Berkeley.EDU (Greg)
Organization: UC Berkeley
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In article <2992@phoenix.Princeton.EDU> tycchow@phoenix.Princeton.EDU (Timothy Yi-chung Chow) writes:
>Two capacitors, with capacitances C1 and C2 respectively, carry
>charges Q1 and Q2 respectively.  Find the total energy stored.
>Now connect the positive plates and connect the negative plates.
>Show that the total energy stored decreases.  Where has the
>energy gone? 

It follows from either Maxwell's equations or consistency arguments
in special relativity that any electrical system has both non-zero
capacitance and non-zero inductance.  If there are no resistors,
the system is necessarily a collection of harmonic oscillators.
If there is (linear) resistance, the system consists of damped
harmonic oscillators.

A (linear) DC system is one in which the resistances are large
enough that the inductances are insignificant.  In the above
question, if there is non-zero resistance, the energy is lost
to heat.  If there is no resistance, the DC approximation
fails and the system is a harmonic oscillator.
--
Greg