Application: Ground resistance of electrodes. A ground electrode is built in the form of a hemisphere, of radius a = 0.1 m, buried in the ground, flush with the surface as shown in Figure 7.39. Calculate the contact resistance (resistance between the wire and surrounding ground). You may assume the ground is a uniform medium infinite in extent, with conductivity σ= 0.1 S/m. Hint. Calculate the resistance between the hemisphere and a concentric conducting surface at infinity. Note. This is an important calculation in design of lightning and power fault protection systems.
