Final answer:
The third prong on some plugs is the ground, providing a path for electricity to the Earth, ensuring safety, and preventing shocks by allowing circuit breakers to trip in case of a fault.
Step-by-step explanation:
The third prong on some electrical plugs is the ground; it provides a low-resistance path to the Earth for extra electrons to discharge. The three-wire system, which includes this ground prong, is an improvement over the older two-wire system without a ground wire. The grounding feature is crucial for safety, as it allows the circuit breaker to trip in case of a fault, such as worn insulation on the live/hot wire touching the appliance case, preventing potential electric shocks. Some modern appliances come with two-prong plugs and are termed doubly insulated, with nonconducting cases that don't require a ground connection. The neutral wire, typically identifiable by its white insulation, is at zero volts relative to the Earth and serves as the return path for the electric current. The proper function of the three-wire system is ensured by the design of standard three-prong plugs that can only be inserted one way into outlets.