conductivity Definition and Topics - 31 Discussions

The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by

k

{\displaystyle k}
,

λ

{\displaystyle \lambda }
, or

κ

{\displaystyle \kappa }
.
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity. For instance, metals typically have high thermal conductivity and are very efficient at conducting heat, while the opposite is true for insulating materials like Styrofoam. Correspondingly, materials of high thermal conductivity are widely used in heat sink applications, and materials of low thermal conductivity are used as thermal insulation. The reciprocal of thermal conductivity is called thermal resistivity.
The defining equation for thermal conductivity is

q

=

k

T

{\displaystyle \mathbf {q} =-k\nabla T}
, where

q

{\displaystyle \mathbf {q} }
is the heat flux,

k

{\displaystyle k}
is the thermal conductivity, and

T

{\displaystyle \nabla T}
is the temperature gradient. This is known as Fourier's Law for heat conduction. Although commonly expressed as a scalar, the most general form of thermal conductivity is a second-rank tensor. However, the tensorial description only becomes necessary in materials which are anisotropic.

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1. Changing the k constant in voltage potential equation?

Summary:: What if you were calculating the voltage potential for a dipole, but underwater? I'm making a predictive model (in R programming) for the voltage potential at any point around a dipole. I need to be able to change parameters, one being the k constant. V=( kpcosѲ)/(r^2). Where V is...
2. Tank Heat Transfer

I'm trying to find a heat transfer equation that includes time. Metal tank, partially filled with liquid. I need to find the time it would take for the temperature on the outside of the tank to drop from θ2 to θ1, given thickness, metal and liquid's properties, and tank dimensions
3. I Is a Copper Conductor Directional?

Hi, A question has arisen an a hifi forum (sorry) that cables can be directional. I dispute this, as the proposed mechanism is diodes in the crystal structure etc. or the drawing process to crate the strands. Assume that it is 99.9% pure copper (CW004A (was C101)) and forms part of a cable with...
4. Sophisticated Experiment (Thermal Conductivity of Housing Materials)

Hi everyone, I am currently a third year University Student in the UK and I'm in the midst of doing my dissertation. My dissertation topic (Effective methods of decreasing the thermal Conductivity of Housing Materials) requires that I produce several experiments to test and analyse a certain...
5. I Understanding L&L's argument, constant current in a crystal

I'm trying to go through chapter III of the vol.8 of Landau and Lifshitz series. (Fortunately the book is uploaded to the archive.org, I guess it is in the public domain.) At page 87 ( << Archive.org link deleted by the Mentors because of copyright violation >> ), they speak about the Joule...
6. Band diagram, conductivity tensor

Hello! Does anyone have an idea of how can I obtain information from a band diagram about the directions along which the system conducts best and worst ? Thank you in advanced! :)
7. A Conductivity and Integration over Fermi-Sphere?

Hi, I am reading "An Introduction of Solid State Physics" from Ibach Lüth and don't understand the integration process. They write $$\sigma=\frac{e^2}{8\pi^3 \hbar} \int df_{E}dE \frac{v^2_x(\bf{k})}{v(\bf{k})} \tau(\bf{k}) \delta(E-E_F)$$  = \int_{E=E_F}^{}df_{E}...
8. Crystal Symmetry Problem

Hello guys! I have to solve a problem about crystal symmetry, but I am very lost, so I wonder if anyone could guide me. The problem is the following: Using semiclassical transport theory the conductivity tensor can be defined as: σ(k)=e^2·t·v_a(k)·v_b(k) Where e is the electron charge, t...
9. B 4 Questions About Lenz's Law Experiment

Hello, I have four questions. As it stands now, I don't have the necessary materials to test this myself, which is how I'd prefer to learn the answer. I still plan on doing this experiment for fun once I can acquire the necessary components. This deals with Lenz's Law. My goal is to maximize...
10. Calculating the conductivity of a solution of HCl and HAc

Homework Statement I need to calculate the specific conductivity k and the resistance R of a cell containitng 0.01 M HCl and 0.1 M acetic acid (HAc). I know the molar conductivity of HAc: Λm = k/c = 5.14 cm2S/mol. I also know Ka (HAc) = 1.795 *10-5. I know the cell constant Kcell = R*k =...
11. Fourier Conduction Law

Homework Statement The question below is asking how long it would take for the cooler side of the handle to heat up till its unbearably hot. I'm having a bit of trouble trying to understand the solution and would like some guidance. I can't seem to get how the ##\Delta T ## that represents...
12. Conductivity of an electrolyte

I know that electric conductivity of metallic conductors increases with decrease in its absolute temperature(kelvin) . But is it the same for electrolytes such as water. Is cold water a better or worse conductor of electricity than warm water at same pressure and concentration.
13. Thermal Physics: Conduction

Homework Statement Homework Equations The Attempt at a Solution Part 1.1) I managed to find the energy needed to melt the ice, before using ΔU = Nf½KΔT to solve for the new temperature, which was correct Part 1.2) Initially tried using ΔQ = mcΔT before realising that I didn't have the...
14. B Equation for Conductivity of Aqueous Solutions

I have found a lot of data and graphs showing conductivity (micro-mhos) vs % by weight of various salt solutions. The salts for which graphs appear particularly linear are those of alkali earth metals - eg sodium, potassium - KI, KBr, KCl etc. Is there a theoretical equation for conductivity vs...
15. Current flow on the surface of a permeability bigger than 1

Hi, Quick description of the problem at hand: spherical perfect conductor around the origin with radius a, spherical shell (with radius b) around it made of a material with given magnetic permeability bigger than 1. Uniform Magnetic field in the area. The solution I am looking at (which I won't...
16. How should I calculate conductivity

Hello, I would like to ask if I have this data from impedance spectroscopy: frequency, Z(im), Z(Real), how should I calculate conductivity ? Should I use R(im) or R(re)?
17. What does Griffith mean by this hint? [Electrodynamics]

I was solving the problems given by Griffith in his book 'Introduction to Electrodynamics' and stumbled across this question. "Because sigma (conductivity of the medium) is a function of position, the equation 7.5 does not hold" --i get this point; current density isn't constant and so its...
18. A How possible is LDA DOS not consistent with experiment?

Usually one would expect through \sigma=ne^2 \tao/m and DOS~1/m to argue that \sigma ~ DOS around Fermi surface. This seems to be a quite fundamental argument and should be expected to hold most of the time. For a quality check, does anybody have experience on how often LDA gives consistent DOS...
19. Graphite touch button

graphite has high conductivity , so i though of making a touch button out of a pencil drawn pattern on the wall.the pattern is shown below. when not touched -resistance between ends of the pattern >200Mohm (exceeds dmm limit) when fully pressed - resistance between ends of the pattern = 1.3...
20. A Where can I find data on electrical conductivity?

Hi folks, I purchased two books on electric transport at the nanoscale and unfortunately I just found theoretical models and formalism... but the actual data from the experiments was not there. So I am curious about it, I am looking for information on nanowires, quantum dots etc and I would...
21. Conductivity of saltwater dielectric vs current

My partner and i have been running experiments for our research in micro algae separation, using a reactor containing aluminum electrodes. we run a 10v current across the electrodes, and flow saltwater between them. we were wondering how changing the conductivity of the saltwater might affect...
22. Conductive Silicon Carbide [Carborundum]

I am trying to create a conductive Silicon Carbide (SiC) heating element. The US patent 650234 "Process of making carborundum articles", filed in 1899 states essentially that crushed SiC crystals can be be glued together (using diluted glue) then sintered. It states that the addition of 15-20%...
23. Hydraulic conductivity Units

Hi I am new to the forum, I am using darcy's equation to model a tumor - tissue medium. In the literature I found that K - Hydraulic conductivity is given by cm^2/(mmHg.s) But in comsol it's given by (m/s) Is there another term involved in this?
24. Are a substance's electrical and heat conductivity related?

For example can an object be very conductive to electricity but be a very poor conductor of heat and vise-versa, or is a good conductor of one always a good conductor of the other and a bad conductor of one always a bad conductor of both? If they are related, then how and why are they connected...
25. Making Carbon pellets with PVA

Hey there. I am making Carbon pellets using polyvinyl alcohol as a binder to help shape the pellets. I would like to measure the pellet's conductivity without being hindered or influence by the conductivity of the PVA. One way to do it is to heat the pellets to 300 degrees and evaporate the PVA...
26. Electrical conductivity of seawater depends on salinity how?

Hi! I am currently trying to determine how the salinity ##S## of a sample of seawater (or, objectively, a salt-water solution) changes its electrical conductivity ##\sigma##. It is clear that they are proportional since the mobility of the ##\text{Na}^{+}## and ##\text{Cl}^{-}## ions plays a...
27. Thermal Physics: Cooling by both Conduction & Convection

Hi all, I am not sure if the is the right place to post the question being new to the forum, but I am looking for some help with a heat transfer experiment that I ran for my honours thesis. Essentially the aim is to determine if warmed saline fluid bags taped to 3 different types of tree barks...
28. How to test a 1.5 pound magnesium anode

Hello my name is Mike Moore and I work for Copperhead Industries, LLC We are a tracer wire manufacture for the underground non-metallic pipe utility sector, natural gas, water, sewer and telecom. We use magnesium anodes for grounding out the far end of the tracer wire system which completes...
29. Parallel electrodes (space charge density, current density)

Homework Statement Two plane parallel electrodes are separated by a plate of thickness s whose conductivity \sigma varies linearly from \sigma_0 near the positive plate to \sigma_0 + a near the negative plate. Calculate the space charge density \rho_f when the current density is J_f ...
30. Mobility of 2D material, sigma=N*e*mu with N surface density

I have measured the conductivity of a 2D material. I want to use σ=N⋅e⋅μ to find the mobility μ=σ/(N⋅e). https://en.wikipedia.org/wiki/Electron_mobility#Relation_to_conductivity I have measured N using a spectroscopic/imaging technique to get a Surface Density with units [cm^-2]. Mobility...