Xref: utzoo sci.electronics:6387 sci.physics:8380
Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mit-eddie!uw-beaver!fluke!strong
From: strong@tc.fluke.COM (Norm Strong)
Newsgroups: sci.electronics,sci.physics
Subject: Re: HV Cap Fun!
Keywords: capacitor,energy,paradox
Message-ID: <8739@fluke.COM>
Date: 1 Jun 89 16:14:05 GMT
References: <4924@m2c.M2C.ORG> <3806@mit-amt> <20772@quacky.mips.COM>
Sender: news@tc.fluke.COM
Organization: John Fluke Mfg. Co., Inc., Everett, WA
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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.

Well. . . 100 microjoules.  But it's the principle that counts.  Right?

}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 ?

The extra energy is dissipated in the form of heat when the current flows
though the series resistance of the capacitor.  If the series resistance
of the capacitor is negligible, it will be dissipated in the form of a
bright flash accompanied by a loud bang (but you won't notice it until the
values get appreciably higher than 10E-4 joules.)
At about 1000 joules, the flash will eat off the end of the wire you use
to connect the capacitors together, and the bang will scare the hell out
of you.    :-)

-- 

Norm   (strong@tc.fluke.com)