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jim hardy
Jan20-13, 09:46 AM
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Nice job Van !!!

Maybe it'll help also to think about what goes on in a good dielectric vs in free space:

Dielectric materials contain polar molecules, ie they have a + and a - end. Water is a good example. Pure water has a dielectic constant around 80, meaning that a capacitor with pure water between its plates would have 80X the capacitance of one with nothing but free space between them.
(Water Molecules image courtesy of these guys: and it's an interesting page.

In presence of an increasing electric field those polar molecules will begin to align with it, abandoning their preferred random orientations, and that takes mechanical work . Discharging the capacitor removes the field so the dielectric relaxes.

That's why oil is used for severe duty AC capacitors - its slippery molecules don't heat up so much as they oscillate with the field. Plastic capacitors will melt in some applications where oil thrive, like commutating or snubbing SCR's.

It's analogous to a mechanical spring. You doubtless noticed the similarity - Van's W = K E^2, for a spring it's K X^2
Doubtless this is oversimplified but it helped me in my early days.

Now - if someone can explain why it is that empty space has a dielectric constant - i'd be much obliged.

old jim