Once an arc is initiated in a gas, the voltage necessary to sustain conduction is _____.

When an arc is initiated in a gas, the voltage necessary to sustain conduction is reduced. This phenomenon occurs due to changes in the physical characteristics of the gas and the arc itself. An arc creates a plasma, a state of matter consisting of ions and free electrons, which significantly lowers the overall resistance to electrical conduction compared to the non-ionized gas.

As the ions are generated and the gas becomes ionized, the electric current can flow more easily because the presence of these charged particles reduces the voltage required to maintain the arc. Therefore, once the arc is established, the energy required to keep it going is lower than what was needed to start it, leading to a reduction in the sustaining voltage.

This concept is crucial for understanding arc behavior in electrical systems and is applied in various applications, such as welding and circuit interrupting devices, where maintaining an arc without excessive voltage is desirable.