An Analysis of Resistance-Characteristics of Static Electric Contacts

This paper considers a conicoid contact as a general case of contact geometry and derives the resistance of the contact when heated by the passage of an electric current. The expressions for the resistance of circular and hemispherical contacts are shown to be particular cases of this phenomenon. The analysis includes bimetal contacts and the impedance of a contact to alternating current. The paper further endeavors to explain low-voltage coherer action in copper contacts in terms of the softening of the parent metal. Experimental results are given to show that, after the rupture of the oxide film, the contact resistance of copper follows a metallic characteristic until melting occurs. Experimental results are also given for the resistance of carbon contacts carrying direct and alternating current.