What is Conductivity: Definition and 400 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.
I have trouble researching whether valence-electrons take part in electrical conductivity. Some sources say that a lower amount of valence electrons lead to an higher electrical conductivity, whilst others say the opposite. And each have their different reasons, for example, lower valence...
I understand that electrical conductivity is a measure of how easily charges are able to move in an object.
During charging by conduction (for conductors), it seems that we simply have to add the charges of both object together and divide by two to obtain the resultant charge of either object...
I have to plot the conductivity dependence of temperature and I have problems with obtaining the right dependency of \mu and n. But let's focus only on carrier concentration first.
For n I used the third equation. From what I understand N_D is a constant. I want my plot to look like this:
But...
Whats its thermal conductivity compared to copper? (as in x times worse than copper)
also, How electrically insulate is it? I'm looking to see if i can use it to encase an entire motherboard in a giant heat sink for a future project where i want to try and cool the entire motherboard to subzero...
One has two same volume blocks of metal, one Aluminium and one copper pushed together. If the Aluminium is instantly heated to 100 degrees C, since it has significantly higher heat conductivity will the copper draw the heat out and at some point be hotter then the aluminium? Or will it just draw...
Okay so this is how it looks like,and there are the given values;
a) I've tried it like this. So I now this formula $$ E = \frac{J}{\sigma} $$ where sigma is the conductivity value. Now to get E we need this formula;
$$ U = \int_{l}{} E \ ds ] $$ Now to get U we can use the ## U = \frac{P}{I}...
I would like to know if spider's web is conductive.
A google search was inconclusive, some sites say that it is conductive, some that it has a high breakdown voltage.
The reason I am asking this is that it seems that I got spiders in my room (honestly I don't know where they are coming from)...
I know k is thermal conductivity but my teacher never told me about effective coefficient of thermal conductivity. I tried googling and found:
$$k_{effective}=\frac{\Sigma{k.A}}{\Sigma A}$$
But I don't know the area to used that information. Is there another approach to do this question?
Thanks
I've tried to explicitly solve the Fourier's equation in cylindrical coordinates but I'm getting some messy integrals which cannot be solved analytically. Additionally my instructor said that there's a neat trick for this problem and it's possible to obtain the answer in a rather elementary...
Good afternoon everyone!
I've learned that thermal conductivity has a form of second-rank tensor. As you know, diagonal components of stress tensor mean normal stress and other components mean shear stress and like that do off-diagonal components of thermal conductivity tensor have some special...
I have a question in regards to a neuromuscular device. Can silicone be combined with hydrogel or the rubber silicone encased in hydrogel to form a wrist watch strap combined with a NMES device. If this is possible how would the hydrogel conduct the NMES device and what is the durability of...
The intrinsic concentration ##n_i## varies with T as
##n_i^2 = A_0T^3e^{\frac{-E_{G0}} {kT}} ## ---> eq1
The mobility ##\mu## varies as ##T^{-m}## over a temperature range of 100 to 400K. For Germanium, m = 1.66 (2.33) for electrons (holes) as per book.
The conductivity is given by ##\sigma =...
We are using the textbook by Jin, "Theory and Comutation of Electromagnetic Fields".
In the section on metamaterialshe derives the dispersion relationship. He shows that when ε'= -ε & μ' = μ
then the dispersion equation γ =\sqrt{jωμ( jωε +σ )} = α + jβ goes to
γ = α = ω \sqrt{μ'ε'}...
We know that,
Conduction Heat Transfer Q = KA(t2-t1)/thickness
K is the coefficient of thermal conductivity. If T2 = 1020°C and T1= 22°C also consider we know A and thickness value.
K depends on temperature. K varies with temperature. For all the materials we have a tabular data of K for...
Hello,
I'm searching for how magnetic field affects the thermal conductivity of the metal (such as steel in solid form). If someone suggests any article about it will be very helpful.
Hi y'all,
I think this is my first time in the chemistry section of this forum, so thank you in advance for your patience with what is (I'm pretty sure) an elementary question. I've googled around for this a bit, but my last acid chemistry study was in 2002 or so, so the reading I am doing is...
In my search, I have been looking for any data that might explain the RF resistance from 3 to 30 MHz range of the two basic types of copper oxides that form on the outside of bare copper wire. I believe these oxides become semiconductors and have large range of impedances. Due to the nature...
Hallo guys,
Im kinda confused about something and hope you can help me. Let me introduce you to it.
we take a look on one Mechanismen to the spin hall effect, skew scattering effect. i just read that you can see this contribution only in the clean Limit. So that's really strange for me cause...
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...
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
Overall thermal conductivity?
for example, there are 3 layers made of different materials, having different thermal conductivities bonded with each other;
conductivity of layer 1= k_1 = 1 W/m-K
thickness of layer 1= t_1 = 0.004 m
conductivity of layer 2= k_2 = 148 W/m-K
thickness of layer 2=...
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...
I worked on a lab experiment that was meant to measure heat capacity but left me with some other questions. The students measured the mass of a cup of liquid nitrogen as it boiled off, recording mass vs time. Then they drop a solid object into the bath, one experiment with a small bit iron...
Can the electron-electron interaction have an impact on the conductivity? Google seems to point out that yes for some 2d materials such as graphene. But what about 3d materials?
Intuitively, any lost momentum by an electron would be gained by another electron, so in average, this e-e...
Hi
When I read the following article:
http://nopr.niscair.res.in/bitstream/123456789/14183/1/IJPAP%2050%286%29%20405-410.pdf
I tried to convert the value of the conductivity for saline in 500 MHz.
At the article, they present the conductivity as ε'' = 70. Which ε'' is the imaginary part of...
(i) Dividing the rod into thicknesses of dx we get discs of area A with lengths=dx so using (****) we have the resistance of a typical disc (between point x' and x'+dx) as:
(1) ##R(x'dx)=\frac{dx}{g(x)A}##
(ii) Using (1) and (*) and the integrating from a to b of the entire rod we get...
A) What are the modern techniques used for enhancing the thermal conductivity of Phase changing materials (PCM) ?
B) what are the negative effects (disadvantages) of using old methods of enhancing thermal conductivity of PCM ? ( construct table )
C) what are the different techniques used for...
Hi, yesterday a professor of mine told me that if you have a temperature gradient along the x-axsis you could have heat flowing in the y direction. Mathematically it is pretty straightforward to find the thermal conductivity tensor required, but in real life can you name some materials that...
Suppose that a large mixture of ice and water is in thermal contact with a reservoir which contains a large quantity of water and steam. Assume that both the ice/water bath and the water/steam reservoirs are otherwise thermally isolated and at a constant temperature. The only contact between...
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...
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...
Does chromium oxide reduce the effectiveness of a faraday cage constructed from stainless steel mesh? I am using mesh that is like insect screen for windows. It will be in moist environment. I appreciate your help!
Hello, my name is Stephen Lanford and I am currently working on a Physics II lab.
I am solving for the thermal conductivity of four materials (glass, plexiglass, pine, and sheetrock) using data from thermal conductivity experiments. The experiments consist of a steam chamber at 100 C, a block...
The common mantra is that when measuring conductivity in solutions the electrodes will build up a polarization layer and disturb the measurement, thus a 4 electrode measurement is used and an alternating current impressed up on the outer electrodes, usually around 1000 hz.
I have been trying to...
Hello,
Just a quick question if I have a let's say a heat source of under a layer of bricks that have a thermal conductivity of 1.6 (W/m/°C.) and on top of the brick a layer of copper with a thermal conductivity of 398 (W/m/°C.).
Is my assumption right that since the layer of brick has such a...
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! :)
Progress
This is the experimental data of thermal conductivity of stainless steel 304L at low temperature. The data is calculated with the Fourier's law of thermal conduction. I checked many times in the excel file and I confirmed that there is no mistake in the calculation. The parameters are...
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}...
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...
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...
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 =...
<< Thread moved from a technical forum, so no HH Template is shown >>
Our teacher gave us a lab, and we have to write a procedure on how to test the electrical conductivity of multiple substances. However, on the materials, all that was written was "electrical conductivity tester", which I'm...