3. Electrical resistivity is a bulk geophysical property of porous soils and roc
ID: 3307711 • Letter: 3
Question
3. Electrical resistivity is a bulk geophysical property of porous soils and rocks. The value of the electrical resistivityis determined by several different physical properties. Give four of these properties and briefly discuss the effect of each of them on the value of the electrical resistivty (2 points) Briefly explain what the terms isotropic, linearly responding, and heterogeneous medium mean·(2 points) Briefly explain the meaning of apparent resistivty and explain how it is determined from a measurement that uses four electrodes. (3 points) The current between two current electrodes at the surface that runs horizontally in the x-direction at some fixed depth level in the subsurface can be influenced by changing the electrode spacing a. The current at any subsurface point for fixed values of x-0, y, and z and variable a is given by 4. 5. 6. ½(x = 0, y, z) _ 2 ((a/2)2 +y2+22)3/ derive for which value of a the current has a maximum. (3 points)Explanation / Answer
Answer to Question 3:
Value of electrical resistivity for porous soils and rocks depends on following physical factors:
Answer to Question 4:
Isotropic Medium: A medium which has the permittivity and permeability of the medium uniform in all direction is called Isotropic medium. i.e. similar properties in any direction
Linearly Responding Medium: A medium which free of saturation and hysteresis is called linearly responding medium.
Homogeneous Medium: A medium which has same composition throughtout its volume is called Homegeneous medium. i.e. same at every point
Answer to Question 5:
Apparent Resistivity:
Apparent Resistivity is the resistivity determined from Ohm's law using potential difference between electrodes for a known value of current. In four probe method to determine apparent resistivity has four probes placed in a line with an equal distance between them. Constant current is passed through two of them and volatge between middle two probes is measured. At a constant temperature, the resistance, R of a conductor is proportional to its length L and inversely proportional to its area of cross section A. This principle is used and resistivity is back calculated.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.