Heating pads contain heating elements that convert electricity
to heat by passing current through a conductor (usually a wire).
This process is variously referred to as resistive heating, ohmic
heating, or Joule heating. The amount of heat generated is
proportional to the square of the applied current multiplied by the
resistance of the conductor. If SI units are employed (amperes for
current and ohms for resistance) the unit of heat energyis called a
joule.