Page:Electricity (1912) Kapp.djvu/85

Rh as oil, glass, mica or paper, it is $$K$$ times smaller. This means that to bring a unit of positive charge to our sphere through such a medium takes $$K$$ times less energy than to bring it through air. In other words, to obtain the same charge an e.m.f. $$K$$ times smaller is sufficient, or, if the e.m.f. is the same, the resulting charge will be $$K$$ times larger. Hence by using a dielectric other than air the capacity of our condenser is increased $$K$$ times. The following table gives the value of $$K$$ for some dielectric materials—

Material Glass Mica Insulating Oil used in transformers Paraffin Wax India Rubber Gutta Percha Paper, as used for power cables Paper, as used in telephone cables Paper, paraffined, as used in condensers Distilled Water Pure Alcohol

K 2—10 5—6 2—1 2.3 2.2—2.8 2.5—4 2.6—3.5 2—2.5 7.2 76 26