Originally posted by Web000x
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The thing is, the dielectric is not primarily there to stop a capacitor shorting itself out, adding a better dielectric simply allows a capacitor to hold more charge before it can either accept no more charge or it does break down and shorts itself out.
The key is the polarisation of the dielectric material. Once polarised, this creates an electric field which counters the field produced by the charges on the plates, so negating some of the forces in action. This way more charge can accumulate on the plates, hence we achieve a greater capacity by employing a dielectric. The more polar the molecules of a dielectric and the easier it is to polarise, the better the dielectric. That is why pure water under certain conditions with it's extremely mobile bipolar water molecule can be a terrific dielectric.
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