# Shared Flashcard Set

## Details

Test 3
Electricity, GPR, Resistivity
71
Geology
Undergraduate 3
12/04/2014

## Cards Return to Set Details

Term
 as wavelength goes up, the signal's ability to penetrate the ground _____, and resolution _____
Definition
 as wavelength goes up, the signal goes deeper, and resolution goes down
Term
 as wavelength goes down, depth of signal _____, and resolution _____
Definition
 as wavelength goes down, the signal can't go as deep, but resolution goes up
Term
 units of conductivity
Definition
 units of conductivity are 1/ohm
Term
 most rocks are poor conductors, so current is carried by ____
Definition
 most rocks are poor conductors, so current is carried by fluids in pore water
Term
 most rocks are poor conductors, so _____ is carried by fluids in pore water
Definition
 most rocks are poor conductors, so current is carried by fluids in pore waters
Term
 in electrical surverys, low frequencies measure _____, while high frequencies measure _____
Definition
 in electrical surveys, low frequencies measure conductivity while high frequencies measure dielectric constants
Term
 Archie's Law
Definition
 Archie's Law is  formation factor = F= (resistivity of rock)/(resistivity of pore water) = aΦ-m
Term
 in Archie's Law, what does each symbol mean?
Definition
 in Archie's Law, formation factor = a*Φ-m Φ is porosity. "a" and "m" are dependent on lithology
Term
 when we say "high frequencies" of electronic surveys, what range of frequencies are we talking about?
Definition
 when we say "high frequency" for electronic surveys, we are looking at 10-1000 MHz
Term
 the goal of examining dielectric properties
Definition
 the goal of examining dielectric properties is to establish a relationship between physical properties of a layer and the radar wave velocity in that layer
Term
 what is dielectric permittivity the same as?
Definition
 dielectric permittivity is the same as dielectric constant
Term
 dielectric constant is a measure of what?
Definition
 dielectric constant is the measure of a material's ability to hold a charge
Term
 dielectric permittivity has units of what?
Definition
 dielectric permittivity has units of farads. A farad is a measure of capacitiance. Capacitance is how much electric potential it takes to acheive one unit of charge. Or how much charge results from one unit of electric potential.
Term
 what property of materials relates how much electric potential leads to how much charge?
Definition
 dielectric permittivity aka dielectric constant aka relative permittivity is the property that has units of farads that relates how much electric potential leads to how much charge
Term
 if a material has a dielectric permittivity of one farad, what does that mean?
Definition
 if one volt (unit of electric potential) results in one columb (unit of charge) then a material has a dielectric permittivity of one farad
Term
 magnetic permittivity is a measure of what?
Definition
 magnetic permittivity is a measure of how much a material gets magnetized when it is placed in a magnetic field
Term
 what property of matierals has units of Henrey's?
Definition
 magnetic permittivity has units of Henreys
Term
 what are units of magnetic permittivity
Definition
 the units of magnetic permittivity are Henrey's
Term
 in a vaccum, radar waves move as fast as ____
Definition
 in a vaccum, radar waves move as fast as the speed of light
Term
 what is the equation for radar wave velocity?
Definition
 the equation for radar wave velocity is  V= c/(square root of (εr*μr))
Term
 what is the skin depth equation?
Definition
 [image]
Term
 what is skin depth
Definition
 skin depth is the depth that waves will travel in a given rock
Term
 the thing about GPR is that the _____ are much higher, so the ____ are much _____.
Definition
 the thing about GPR is that the velocities are much higher, so the wavelengths are much shorter
Term
 I do GPR and acoustic surveys in a granite layer. In Survey one, the wavelength for my waves is 50 meters. In Survey two, the wavelengths for my waves is .6 meters. Which survey is GPR, and which is acoustic?
Definition
 GPR has shorter wavelengths  Acoustic has longer wavelengths   Survey 1 is acoustic  survey 2 is GPR
Term
 relationship between vertical resolution and wavelength
Definition
 the relationship between vertical resolution and wavelength is that vertical resolution is about a quarter of wavelength
Term
 as you use GPR to anaylze a system with an uneven boundary layer, what is an issue that will create more error?
Definition
 scattering and focussing are problems you run into when you use GPR to anaylze a system with an uneven boundary layer
Term
 what property of materials does an induced potential survey measure?
Definition
 an induced potential survey looks at the chargeability of materials
Term
 what electricity survey examines the chargeability of materials?
Definition
 induced potential surveys look at the chargeability of materials
Term
 what is the application of induced potential electrical survey?
Definition
 induced potential surveys are used for base metal exploration
Term
 how do you do an induced potential survey?
Definition
 an induced potential survey is done by applying an electric field to the ground, then turning it off. then you measure if the ground is still conducting electricity
Term
 in an induced potential survey, the time that rocks are still charged after you turn off the electric field is on the scale of _____
Definition
 in an induced potential survey, rocks will be charged after you turn off the electric field on a scale of seconds
Term
 in an induced potential survey, the distance that the charge travels after you turn of the electric field is a function of  _____
Definition
 in an induced potential survey, you apply an electric field then turn it off. The distance that the charge travels through the ground afterwards is a function of frequency
Term
 why can't you use a standard resistivity array for a induced potential method?
Definition
 you need to record the charge of the ground for several seconds, which a standard resistivity array cannot do
Term
 what electrical technique do we use for base metal exploration?
Definition
 we use induced potential for base metal exploration
Term
 what does the spontaneous potential electrical survey look for?
Definition
 the spontaneous potential electric survey looks for an oxidizing/reducing boundary
Term
 what is the application of the spontaneous potential electric survey?
Definition
 the spontaneous potential electric survey is used for mineral exploration
Term
 what electric survey is used for mineral exploration?
Definition
 spontaneous potential is the electric survey used for mineral exploration
Term
 what signal does the magneto-telluric electrical method look at?
Definition
 the magneto-telluric electrical method is looks at electric flow caused by charged particles flowing from the ionosphere
Term
 the magneto-telluric method has what application?
Definition
 the magneto-telluric method is used to look at crustal/lithosphere scale studies. It is especially good at looking under basalts in sedimentary basins
Term
 what electrical method is used for crustal/lithosphere scale studies?
Definition
 the magneto-telluric method is used for crustal/lithosphere scale studies
Term
 with the magneto-telluric methods, you need a base station with _____
Definition
 for the magneto-telluric method, you need a base station with two electrodes at 90° from one another. This is how you measure variations in voltage
Term
 for _____ surveys, you have a base station with electrodes at 90° to measure variations in voltage
Definition
 for magneto-telluric surveys, you have a base station with electrodes at 90º to measure voltage
Term
 definition of conductivity
Definition
 conductivity is defined as "the degree to which a material conducts electricity"
Term
 conductivity calculated as _______
Definition
 conductivity is calculated as "the ratio of electric current density to the electric field that generated them"
Term
 this property is defined as "the ratio of current density to the electric field"
Definition
 conductivity is defined as "the ratio of current density to the electric field"
Term
 this property is the reciprocal of resistivity
Definition
 conductivity is the reciprocal of resisitvity
Term
 what is the difference between active and passive resistivity/electromagnetic surveys?
Definition
 active surveys: you generate a current and measure how it travels through the subsurface Passive surveys: you measure natural currents
Term
 what is induced polarization?
Definition
 induced polarization is when you apply a current to the ground and then make measurements
Term
 electromagnetic surveys all consist of what?
Definition
 all electromagnetic surveys involve generating a magnetic field, which generates an electric field which you measure with coils
Term
 ohm's law states that ____
Definition
 ohm's law states that the current flowing through a material is proportional to the potential applied to that material  V is proportional to i  V is voltage, a measure of potential  i is current flow
Term
 which law states at V is proportional to i
Definition
 ohm's law states that V is proportional to i  V is voltage, a measure of potential i is curent
Term
 what is the constant of proportionality between V and i?
Definition
 the constant of proportionality between V and i is resistance, denoted as R. resistance has unit of ohms V=R*i
Term
 resistance is related to potential and current how?
Definition
 resistance is the proportionality constant between potential and current.  V=i*R
Term
 units of resistance
Definition
 units of resistance are Ohms
Term
 the law of cables states _____
Definition
 the law of cables states that resistance is proportional to the length of cable it is running through (L) and inversely proportional to the cross-sectional area of the cable it is running through.
Term
 what is the constant of proportionality for resistance and length/area
Definition
 the constant for proportionality of resistance and length/area is resistivity, denoted as ρ ρ = (R*L)/A
Term
 units of resistivity
Definition
 units of resistivity are ohm-meters
Term
 resistivity is the constant of proportionality between ____ and ____
Definition
 resistivity is the constant of proportionality between resistance and length/area
Term
 what is the connection between length of a current flow line and the time it takes the signal to be communicated?
Definition
 the longer the current flow line, the longer it takes the signal to be communicated
Term
 what kind of diagram could you look at to see how relatively long it takes different current paths to go from one point to another
Definition
 a current flow diagram shows current paths. the longer currents paths take longer to communicate signal compared to shorter ones
Term
 You are looking a current flow diagram. The current paths goes to a new layer and bends towards the vertical. What do we know about the lower layer?
Definition
 when a current enters a new layer and bends towards the vertical, the new layer is higher resisitivity
Term
 what is the change in resistivity data as electrodes are moved farther and farther away in a two layer system?
Definition
 as electrodes get farther and farther away, apparent resistivity gets closer and closer to the resisitivity of the lower layer
Term
 in a current flow diagram, path density is related to _____
Definition
 in a current flow diagram, high path density means high current density
Term
 what is the biggest application of resistivity surveys
Definition
 the biggest application of resisitivity surveys is finding how much water is in different layers, which we can deduce permeability from
Term
 resistivity surveys don't give you distinct layers, they give you _____
Definition
 resitivity survey's don't tell you what layers are present, they simply give you pseudosections
Term
 what kind of surveys always involve predictive modeling after you get information from the earth?
Definition
 Resistivity studies only give you apparent velocity and pseudosections, so you have to use predictive modeling to see what the information is actually telling you
Term
 after you get information from the earth from resisitivity surveys, this is the next step
Definition
 you always finish resisitivity surveys with predictive modeling
Term
 what is the difference between forward and reverse modeling?
Definition
 forward modeling is making a model based on what you expect to see before you survey the earth.  inverse modeling is looking at the data from a survey and finding a model to match
Term
 what does InSAR look at?
Definition
 InSAR looks at elevation
Term
 is spontaneous potential active or passive?
Definition
 spontaneous potential is passive
Term
 what do you need for spontaneous potential?
Definition
 the setup for spontaneous potential is simply two electrodes
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