For which reason does a Kelvin Bridge have 4 leads?

The presence of four leads in a Kelvin bridge primarily serves to eliminate extra impedance during measurements. This design is particularly useful when measuring low resistances, where the lead resistance can significantly affect the accuracy of the readings.

By using four separate leads – two for carrying the current and two for measuring the voltage – the Kelvin bridge minimizes the impact of lead and contact resistances on the measurement. The current leads are responsible for driving the current through the resistance being measured, while the voltage leads measure the potential difference across the component without being impacted by the resistance of the leads themselves. This configuration ensures that the measurement accuracy is improved, particularly in applications where even small resistances are critical.

Other options do not directly align with the specific function of the Kelvin bridge's four-lead design. The method is not designed for high voltage measurement, it does not specifically focus on AC measurements, and while it may contribute to a simpler measurement process in some respects, the key advantage is the reduction of extra impedance in the measurement circuit, ensuring more precise readings.