How does a continuity tester show that a circuit is complete?

A continuity tester is a tool used to verify whether an electrical path is complete, which is essential for troubleshooting electrical circuits. One of the most common ways it indicates a complete circuit is by lighting a lamp. When the circuit is complete, the electrical current flows through the tester, causing the lamp to illuminate. This visual indicator (the lit lamp) provides immediate feedback to the user that the circuit is continuous and functional.

While the other options might suggest different methods of testing or show some kind of response, lighting a lamp is a direct indication of continuity. For example, producing a sound may not be a feature of all continuity testers, and even if it were, a sound alone does not visually confirm that electricity is flowing through the circuit the way a lit lamp does. Similarly, displaying a voltage reading could indicate power presence but does not necessarily confirm that the circuit is uninterrupted. Changing color could apply to certain types of testing tools but is not a standard feature of most continuity testers and lacks the immediacy and clarity provided by a lamp lighting up. Thus, a lamp lighting up is the most reliable and common method to show that a circuit is complete.