When does a short circuit occur?

• A. When the resistance drops to near zero
• B. When the resistance increases
• C. When the current exceeds rating
• D. When there is no power supply

Answer: (A)

A short circuit happens when current finds a path of near-zero resistance, bypassing the intended load. This is why the right answer is that a short occurs when resistance drops to nearly zero: with a given power source, I = V/R means a very small R produces a very large current, creating a fault condition as current surges through an unintended, low-resistance path. In real circuits, this can trip fuses or breakers and cause wiring to overheat.

Resistance increasing would reduce current and not produce a short. Exceeding the circuit’s current rating is a consequence of a short, not the defining condition. No power supply means no current flows, so there isn’t a short.