In the Wenner electrode configuration used for surface electrical resistivity prospecting of groundwater, the four collinear electrodes are arranged such that:
Options:
(A) All four adjacent electrodes have strictly equal spacing $a$
(B) The inner potential electrodes remain fixed while outer current electrodes move
(C) The potential electrode spacing is at least five times the current electrode spacing
(D) Only three electrodes are placed on the ground surface
Answer Key:
A
Step-by-Step Solution & Explanation
In the Wenner array, four electrodes ($A, M, N, B$) are driven into the ground in a straight line with uniform equal spacing: $AM = MN = NB = a$. The apparent resistivity is calculated as $\rho_a = 2\pi a \frac{\Delta V}{I}$.