|MadSci Network: Chemistry|
Those are some great questions you pose! I'll try and answer each question as completely as possible.
A capacitor, like an inductor, or even a spring, is capable of storing energy. A spring stores energy as mechanical strain, an inductor in a magnetic field. A capacitor stores energy in an electric field. In all of these cases, the stored energy must come from an external source. For a spring, it comes from mechanical stress, in an inductor, energy comes from externally applied electrical current. You can guess where the energy stored in a capacitor comes from.
For ideal components, energy storage is perfect, meaning no energy is lost. This is, of course, not true in the real world. Energy is lost in electrical resistance and leakage current. This shows up as heat. Inductors with permeable cores may also lose energy due to hysteresis losses. Hysteresis is like memory, ferromagnetic materials exhibit this phenomenon. Hysteresis losses also result in heat. Some dielectrics can exhibit a memory effect like ferromagnetic materials and also lose energy in heat, but it is not nearly as pronounced in dielectrics. I don't believe pure water does this, the only losses are due to leakage currents. Electrical engineers often choose capacitors based on dielectric losses in certain cases like radio frequency (RF) power amplifiers.
To summarize, heat in capacitors is caused by losses. Perfect (lossless) dielectrics do not heat up, but there are no perfect dielectrics. Pure water is actually a very good insulator, so very little energy is lost as heat. The energy is stored in the electric field and can be returned an external sink a later time with very little loss.
I hope I have answered your questions, if not, drop me a line at firstname.lastname@example.org
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