Electrical Resistivity Method MCQ Quiz

The electrical Resistivity Method is commonly used in engineering and groundwater investigations. This method involves measuring the electrical resistivity of subsurface materials to determine their composition and properties. It helps in identifying the presence of underground structures, such as faults or fractures, which can be crucial in engineering projects. Additionally, the resistivity method is used to locate groundwater resources and assess their quality and quantity. By analyzing the resistivity data, geologists and engineers can make informed decisions about the feasibility and design of construction projects and effectively manage groundwater resources.

The resistivity along a bedding plane is less than the resistivity across it because the bedding plane typically consists of loosely packed sediments or fractures that allow for easier flow of electrical current. This results in a lower resistance along the bedding plane compared to the resistance across it, where the current has to traverse through a greater distance of rock or material with higher resistivity.

The electrical conduction mechanism in sedimentary rocks is usually electrolytic. This means that the rocks can conduct electricity through the movement of ions within their structure. This is different from electronic conduction, which involves the movement of electrons. Sedimentary rocks are composed of various minerals and can contain water or other fluids within their pore spaces. These fluids can act as electrolytes, allowing for the flow of ions and the conduction of electricity.

The Principle of Reciprocity states that the response of a system to a source depends only on the relative position of the source and the receiver. This principle is applicable to both homogeneous and non-homogeneous earth because it focuses on the relative positions and does not consider the specific characteristics of the medium. Therefore, whether the earth is homogeneous (uniform composition) or non-homogeneous (varying composition), the Principle of Reciprocity can still be applied to analyze the response of the system.

The Formation Factor is calculated by dividing the resistivity of the matrix by the resistivity of the water. In this case, the resistivity of the matrix is 100 ohm-m and the resistivity of the water is 20 ohm-m. Therefore, the Formation Factor is 100/20 = 5.

The quantity (h1/ρ1) + (h2/ρ2) + (h3/ρ3) represents the longitudinal conductance. This is because conductance is the reciprocal of resistance, and the given expression involves the sum of thicknesses divided by resistivities. Conductance is a measure of how easily electric current can flow through a material, and in this case, it represents the combined conductance of the three layers of the earth.

In a 4-layer subsurface model, the combination of HQ type electrical resistivity sounding curves is not possible. This is because the H-type curve represents a high resistivity layer, while the Q-type curve represents a low resistivity layer. These two types of curves are contradictory and cannot exist together in the same model.

Resistivity profiling is taken at a 90-degree angle to the strike because it provides a cross-sectional view of the subsurface, perpendicular to the strike direction. This allows for a comprehensive understanding of the resistivity variations at different depths. On the other hand, resistivity sounding is taken at a 0-degree angle to the strike, which means it is parallel to the strike direction. This method provides information about the resistivity variations along a single line, helping to determine the lateral continuity of subsurface layers.

The resistivity of conducting metallic sulfides varies from 0.00001 to 0.1 ohm-m. This means that different metallic sulfides can have resistivities within this range. It suggests that metallic sulfides can have relatively low resistivity values, which indicates their ability to conduct electricity efficiently. The range provided also implies that there can be variations in the conductivity of different metallic sulfides, with some being more conductive than others.

The resistivity of acidic igneous rocks is not necessarily less than the resistivity of basic igneous rocks. The resistivity of a rock depends on various factors such as its composition, porosity, and moisture content. While it is true that some acidic igneous rocks may have lower resistivity due to their higher water content, it is not a general rule. Similarly, some basic igneous rocks may have lower resistivity depending on their specific characteristics. Therefore, it is incorrect to say that the resistivity of acidic igneous rocks is always less than that of basic igneous rocks.

It generally has the range 1-100 ohm-m

The two-electrode configuration has the maximum depth of investigation for homogeneous earth. This is because in this configuration, one electrode is used to inject current into the ground, while the other electrode is used to measure the potential difference. This setup allows for a deeper penetration of the electric field into the earth, resulting in a greater depth of investigation. In contrast, the three-electrode configuration and the Wenner and Schlumberger configurations involve multiple electrodes, which can limit the depth of investigation.

The Pole Pole 4-electrode configuration is best suited for Archaeological Investigations. This configuration involves placing two current electrodes close together and two potential electrodes further apart. This setup allows for a deeper penetration into the ground, making it ideal for detecting buried archaeological features or structures. Additionally, the Pole Pole configuration provides good resolution and can accurately map the subsurface, helping archaeologists locate and identify potential archaeological sites.

The formation factor is a measure of the ability of a rock formation to transmit electrical current. It is directly related to the porosity of the rock, which is the measure of the volume of voids or openings in the rock. A higher porosity indicates a higher formation factor, meaning that the rock has more voids and can allow for better electrical conductivity. Therefore, the formation factor is related to the porosity of the rock.

The correct answer is K Type. The K Type VES curve represents a three-layer sequence with moist soil on top, followed by freshwater saturated coarse sand in the middle, and clay at the bottom. In this type of curve, there is a sharp increase in resistivity from the moist soil to the freshwater saturated coarse sand, indicating a change in lithology. The resistivity then decreases significantly when reaching the clay layer due to its high conductivity. This pattern is characteristic of the K Type curve.

The coefficient of anisotropy measures the degree of anisotropy or the extent to which a material's properties vary with direction. A value between 1 to 2 suggests that the material is moderately anisotropic, meaning that its properties vary significantly with direction but not to an extreme extent. This range indicates that the material has some level of directionality in its properties, but it is not highly directional or isotropic (uniform in all directions).

The Wenner electrode configuration acquires maximum vertical resolution because it has the largest electrode spacing compared to the other options. This larger spacing allows for better depth penetration and the ability to detect subtle changes in the subsurface. The Schlumberger configuration has the smallest spacing, resulting in lower vertical resolution. The Pole Dipole and Half Wenner configurations have intermediate spacing and therefore lower vertical resolution compared to the Wenner configuration.

The limiting depth of electrical sounding refers to the maximum depth that can be accurately measured using this method. In this case, the correct answer is "more than 10 km," indicating that electrical sounding can accurately measure depths greater than 10 kilometers.