Mobile Electronics Certified Professional (MECP) Advanced Practice Test

When performing a voltage measurement with a digital multimeter (DMM) and the leads are reversed, the meter will display the voltage value with a negative sign. This is because the DMM measures the voltage as the potential difference between the two probes. In a standard scenario, the red lead is connected to the more positive point, and the black lead is connected to the more negative point, resulting in a positive voltage reading. However, when the leads are reversed, the black lead is at the higher potential, and the red lead is at the lower potential. As a result, the DMM effectively "sees" the voltage as the negative of what it would normally read, thus indicating the measurement with a negative sign. This behavior is fundamental to how digital multimeters interpret voltage measurements, making it clear that lead polarity plays a crucial role in determining the sign of the measured voltage.