The Force on the Cathode of a Copper Arc

Abstract

The force on the cathode in the electric arc, previously examined either in air at atmospheric pressure or in vacuum, is studied as a function of pressure. For the copper arc in nitrogen the force is found to remain of the order of magnitude of the values observed in air down to a pressure of about 5 mm, and then to increase sharply but smoothly to the much larger forces observed in vacuum. Various aspects of the arc are examined in this transition region. Curves showing force as a function of current at various pressures of hydrogen and nitrogen are given. A brief study of the stability of the vacuum arc is included, as well as a summary of the various theories put forward to explain the phenomenon.