What is a short circuit?

• A. A fault path with very low resistance causing excessive current.
• B. A circuit with an open switch.
• C. A device that converts AC to DC.
• D. A protective device that opens on fault.

Answer: (A)

A short circuit is a fault path with very low resistance that causes an excessive current to flow through the circuit. When the resistance provided by the path is tiny, Ohm’s law (I = V/R) means the current becomes extremely large, often leading to overheating, component damage, or tripping of protection devices. The other descriptions refer to scenarios that do not create a low-resistance fault path: an open switch stops current entirely; a device that converts AC to DC is a rectifier, not a fault; and a protective device that opens on fault is meant to interrupt the fault, not to form the fault path.