An electrical arc is the passage of electrical current through a medium (like air) that has become ionized and thus electrically conductive. This ionization typically happens when the electric field strength across the gap becomes high enough.

Arc Production with AC and DC Current

An arc can be sustained by both types of electrical currents:

• AC (Alternating Current): AC current periodically changes direction. An arc initiated by AC can be maintained through each half-cycle as the voltage rises and causes ionization. While the current passes through zero twice per cycle, the residual ionization often allows the arc to re-establish quickly in the next half-cycle.
• DC (Direct Current): DC current flows in a constant direction. It can easily establish and sustain an arc across a gap, provided the voltage is sufficient to cause ionization and the current is high enough to maintain it. This is commonly observed in DC welding and circuit breakers.

Since both AC and DC currents possess the ability to ionize a medium and sustain a discharge, an arc can be produced by either type.

Conclusion

Based on the principle that both alternating and direct currents can cause ionization and sustain an electrical discharge, the correct answer is that an arc can be produced by either AC or DC current.