If a four-foot ground rod has a resistance of 40 ohms, what will be its resistance if extended to eight feet?

When a ground rod is extended, its length increases, which generally leads to a decrease in resistance due to the greater contact area with the surrounding soil. In this case, the initial four-foot ground rod has a resistance of 40 ohms, and when that ground rod is extended to eight feet, the resistance effectively decreases.

The resistance of a rod can be analyzed through the principles of resistivity and the geometry of the rod. The resistance of a conductive path is inversely proportional to its length; as length doubles, the resistance will not double but rather decrease. This reduction can be estimated based on a simple linear relationship, where doubling the size can reduce the resistance by half under ideal conditions. Therefore, extending the ground rod from four to eight feet suggests significant decrease in resistance.

With 40 ohms at four feet, a reasonable estimate for the resistance at eight feet could be around half, which would be 20 ohms. However, practical factors come into play in real-world applications, and soil conditions can influence actual measurements.

The option of 24 ohms suggests a minor consideration of varying conditions than a purely ideal assumption, making it the more suitable answer given typical environmental and material variances. Hence, the correct answer reflects a common