EOSC252 - Exercise 9

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Name: 1. Introduction EOSC252 - Exercise 9 Dielectric properties This is really nothing more than a multiple choice / short answer quiz-style assignment.

1 Name: 1. Introduction EOSC252 - Exercise 9 Dielectric properties This is really nothing more than a multiple choice / short answer quiz-style assignment. You will need to have done the readings about dielectric properties, and there is one short reading at the UBC-GIF (Geophysical Inversion Facility) web site. 1.1 Learning goals for this exercise Identify how each of the four different types of polarizing mechanisms affect varying electromagnetic fields within materials. Explain how the various characteristics of geologic materials affect the behavior of low frequency and high frequency electromagnetic waves inside the materials. Explain the distinction between chargeability and dielectric permittivity in terms of the fundamental mechanisms defining these two properties. Apply fundamental ideas about frequency dependant dielectric permittivity to predict or explain some behaviors of GPR (ground penetrating radar) measurements. 2. The 26-question exercise: For Multiple Choice questions just circle your chosen answer or answers. Fill in blanks for short answer questions within the spaces provided. 1. We have studied how characteristics of geological materials affect the value of the following physical properties. Select ALL that do NOT depend on how rapidly we vary the energy used to measure the value. a) Density b) Porosity c) Permeability d) Wettability e) Resistivity f) Dielectric permittivity g) P-wave velocity h) S-wave velocity 2. Which of these polarizable components will be able to follow along as an electric field is alternated at 10 5 (100,000) Hertz? Pick ALL that apply. 3. Which of these polarizable components will be able to follow along as an electric field is alternated at 10 7 (10,000,000) Hertz? Pick ALL that apply. 4. What gets forced into a new orientation when the material experiences the application of a NON-VARYING electric field?

2 5. Conductivity, "sigma", describes the capacity for a material to allow current to flow under the influence of a voltage difference. Complete the analogous phrase: Permittivity, "epsilon", describes the capacity for a material to become under the influence of a (an) field. 6. The dielectric constant for a material, "kappa", and it's permittivity, "epsilon", are often used interchangeably. Conceptually this is OK, but it is very important to be careful which is being used because values are very different. The value of the constant used to obtain one from the other is (3 decimal places) x to the power, in units of. This constant in fact is the permittivity of 7. Select correct terms or values from the long list and fill in the blanks with corresponding letters for each of the four missing parts in these sentences: The A[ ] part of B[ ] represents energy dissipation during charge redistribution. Figure C[ ] in Gueguen tells us that frequencies of D[ ] Hz will most effectively loose energy in water at 0 degrees C. a) 1x10^11 b) smallest c) permittivity d) 2x10^11 e) conductivity f) IX.7 g) 2x10^10 h) largest i) IX.3 j) 2x10^9 k) imaginary l) IX.4 m) real n) temperature o) 1x10^9 p) IX.6 q) 1x10^10 8. Which polarization process contributes to the dielectric permittivity, epsilon, equally for all frequencies less than optical? 9. Which polarization process contributes to the dielectric permittivity, epsilon, by an amount dependent on the type of non-metallic elements in the material (or mineral)? 10. Which polarization process contributes to the dielectric permittivity, epsilon, when materials are non-uniform?

3 11. (REQUIRES READING A SHORT 3-PG WEB RESOURCE) Go to click on 2. Foundations, then d. Physical properties then 2. Chargeability and read the Introduction section (~3 paragraphs). Which phenomenon discussed by Gueguen is related to this physical property called chargeability? (NOTE: Ignore the "See the Electrical Resistivity chapter" instruction.) a) effects due to polarization at optical freqencies b) effects due to polarization of individual atoms c) effects due to polarization of water molecules d) effects due to polarization of gaseous components e) effects due to polarization of charges within pore spaces 12. Figure IX.3 in Guguens Ch 9. and a similar dielectric permittivity spectrum shown in the GPR writeup in DielectricPermittivityGPR.pdf are not quite the same. What information is NOT in the Gueguen figure but IS in the other? a) information about which frequencies are most lossy for three types of polarization. b) the relationship between dielectric constant, "kappa", and the permittivity, "epsilon". c) descriptions of the types of electromagnetic energy for each range of frequencies. d) relative amplitude of contributions to permittivity due to all forms of polarization. e) names of polarization mechanisms 13. What does it mean to say that the imaginary component of dielectric constant, Kappa'', describes how lossy a situation is? a) It means Kappa'' gives information about which polarization mechanism contributes the most to permittivity. b) It means Kappa'' gives information about the rate at which EM energy dissipates as it propagates into the material. c) It means Kappa'' gives information about how fast EM energy looses speed in the material. d) It means Kappa'' gives information about which frequencies get lost as EM signals progress into the material. e) It means Kappa'' gives information about which mechanisms loose touch with the oscillating E-field. 14. Why would GPR measurements NOT respond to variations in chargeability? A sentence or two is all that is needed. 15. The relaxation time, tau, for a molecule (eg water) is a measure of the time required for the molecule to rotate, or equivalently, to revert to normal after being rotated. It is proportional to molecular radius and viscosity, and inversely proportional to temperature. If measured at a frequency omega=1/tau, water s dielectric permittivity (real part) would be a) maximum b) minimum c) changing most rapidly d) zero e) "infinity"

4 16. If measured at a frequency omega=1/tau, water s dielectric permittivity (imaginary part) would be a) maximum d) zero b) minimum e) "infinite c) changing most rapidly 17. The Debye model helps predict a materials dielectric constant as a function of frequency when only one polarization process is acting. This model for dielectric permittivity involves two fixed permittivities. These are (select both that are true) a) Permittivity of the material at very low frequencies b) Permittivity of the material at very high frequencies c) Permittivity of the material at the relaxation frequency d) Permittivity at zero degrees C. e) Permittivity at 100 degrees C. 18. The Debye model for permittivity as a function of frequency is limited for use with most materials because: a) it predicts constant values at commonly used GPR frequencies b) water is a prominent component of many materials c) we don t know the relaxation time for most materials d) more than one polarization process is usually occurring e) it is only valid for dipolar polarizations 19. Write one or two sentences that speculate as to why kappa0 is temperature dependent but kappainfinite is not. 20. In the figures of GPR data at an environmental waste site, what is the most likely reason that the zone under the top of clay featureless?? (Images are at the end of the GPG-Dielectrics- GPR-8pgs.pdf readings file.) a) That zone did not absorb energy so no signals were visible. b) The clay layer absorbed more of the EM energy than materials over the waste oil basin. c) Material properties caused GPR signals to reflect off the top of clay layer so nothing can be seen under it. d) Physical properties of the water table caused GPR signals to be absorbed. e) There are no changes in properties within that featureless zone. 21. The glaciology images demonstrate that echoes from GPR signals can be seen after traveling through over 200 meters (both there and back) of ice. What does that suggest about the physical properties of ice? (Images are at the end of the GPG-Dielectrics-GPR-8pgs.pdf readings file.) a) Signals must be traveling faster in ice than in most geological materials. b) Signals must be traveling slower in ice than in most geological materials. c) Ice must be more conductive than most geological materials. d) Ice must be more resistive than most geological materials. e) Ice must have a higher permittivity than most geological materials f) Ice must have a lower permittivity than most geological materials

5 22. fractures What do you think it is about the material properties of rocks and fractures that allows GPR to be useful for finding the location and orientation of fractures using a borehole GPR system? 23. True or False? The velocity for 0.5 Ghz GPR signals in ALL clays can be estimated using Don't guess - use relations and values from the table in the DielectricPermittivityGPR.pdf document to prove your answer. ALSO NOTE the conductivity units in the table are given in milliseimans/meter; that is, 1 ms/m = S/m. Also, Ghz = 10 9 Hertz a) True b) False Hint: only one calculation is needed; you simply have to choose the right values to show an assumption necessary for this type of velocity estimate does not hold. 24. True or False? The velocity for 0.5 Ghz GPR signals in SOME clays can be estimated using Same hints and comments as previous question. a) True b) False 25. Use the table of values in the DielectricPermittivityGPR.pdf document to help put the following materials in order of highest to lowest MAXIMUM velocity for GPR signals (i.e. do not use the Vavg column): highest velocity:, 2., 3., 4., 5., lowest velocity: a) granite b) water c) clay d) wet sand e) dry sand f) shale 26. Use the table of values in the DielectricPermittivityGPR.pdf document to help put the following materials in order of deepest to shallowest penetration for GPR signals: deepest:, 2., 3., 4., shallowest. a) limestone b) clay c) granite d) ice e) shale END.

1. Resistivity of rocks

1. Resistivity of rocks RESISTIVITY 1) Resistivity of rocks 2) General principles of resistivity surveying 3) Field procedures, interpretation and examples 4) Summary and conclusions INDUCED POLARIZATION 1) General principles