When measuring across the terminals of a diode, a reading of zero indicates what condition?

When measuring across the terminals of a diode, a reading of zero volts indicates that the diode is conducting. This occurs when the diode is forward-biased, allowing current to flow through it. In this state, the voltage drop across a conducting diode is typically around 0.7 volts for silicon diodes and approximately 0.3 volts for germanium diodes; however, if the measurement is taken under certain conditions—such as using an ohmmeter with a lower test voltage or in specific circuit configurations—it can yield a reading that appears closer to zero due to the internal resistance of the diode being very low in the conducting state.

In contrast, if the diode is open, there would be no continuity, and the reading would indicate infinite resistance. Similarly, if the diode is reverse-biased, it would block current flow, resulting in a high reading, and if it is forward-biased without load, the voltage might not exactly measure zero but rather show a low value reflecting the diode's forward voltage drop. Hence, seeing a reading of zero is primarily indicative of current flowing freely through the diode, confirming it is in a conducting state.