Geothermal power stations tap aquifers heated by contact with hot rocks in volcanic regions-or, in hot but dry spots, they pump water past such rocks to heat it up.

Doubling hf-current results in a doubling of current density and a fourfold heat provided that the area of effective contact between the tissue ang the electrode remains constant.

Contact failure can occur when excessive heat or a high current or voltage pulse causes the contacts to weld together, resulting in short circuits.