By electrical heating capacitor I am guessing you mean the tuning capacitor used in a high frequency induction heater.
Trying to think back too many years to college, but if I remember the capacitor in an induction heating circuit is used to establish the resonant frequency of the induction heating coil to create as large as possible sinusoidal current.
If you Google “high frequency induction heating” you should find some explanations of the science.
Unfortunately my memory of this is a bit to fuzzy for me to try to go in to the mathematics but you could try looking out for a book entitled “Electronic Circuit Theory & Technology” by John Bird, ISBN 0 7506 5784 7 and look at chapter 43 Magnetically coupled circuits.