Conductivity Definition and 382 Threads

Several papers (eg. Di Xiao, et. al, Berry phase effects on electronic properties, RevModPhys, 82,2010)mentioned a formula to calculate the Hall conductivity(See the picture).This formula is used in an two dimensional system, v1 and v2 are velocity operators in x and y direction, Phi0 and PhiN...

Homework Statement Given an insulating case outer surface at 25C, radiates heat to surroundings at 20C. Find temperature inner surface. Homework Equations The Attempt at a Solution The heat is conducted through a thickness of 2.5mm, with a temperature difference of 5oC. Thus...

Homework Statement Estimate the electrical conductivity, at 135°C, of silicon that has been doped with 3 x 1024 per meter cubed of aluminum atoms. Assume values for electron and hole mobilities of 0.03 and 0.007 m2/V-s, respectively. Homework Equations σ=|e|(ne*μe+nh*μh)...

Hi all Homework Statement The Debye temperature of argon is 92 K and that of silicon is 345 K. Rank the following in order of thermal conductivity (largest value first): (i) A 1 cm3 cube of silicon at 6 K (ii) A 512 mm3 cube of silicon at 2 K (iii) A 1 mm3 cube of argon at 4 K (iv)...

How does humidity affect conductivity of air? I am asking this that because I read that dry air is better insulator than normal air.

I've tried searching for it but while there are a lot of hits on the fact that graphene's conductivity is high, there seem to be very few on how the conductivity is actually measured. Would you use the same method as you do with metal wires? Using cross sectional area, length, an ohmmeter...

I had a random idea about the effect of cosmic rays on graphene's conductivity. I found out that cosmic rays would create defects in graphene over time. How many of these defects would significantly reduce the conductivity of graphene? How do I go about calculating how much time the graphene...

I'm interested in modeling a system where the material varies along its length, thus the conductivity coefficient would be a function of both T, and x. k(T,x). For starters, if I assume negligible change w.r.t T, then he heat diffusion equation would be d/dt(k(x)dT/dx)=0. Correct? What if k just...

I am working on some basic calcs for heat transfer from polyethylene pipe. My numbers are not working out right so I need a little refresher. The PE pipe would have a TC of about .46 W/(m.*C). to get to BTU/(hr.ft.*F), I mult by .5779 to get .266. Assuming 10sf of PE pipe, and let's...

I can't derive it properly even though it should be easy: From Newtons 2nd law: m dv/dt = -eE => v(t) = -meEt + v(0) (the latter will average out when taking average) Now the Drude assumption: An electron will on average travel a time τ before being scattered and starting its motion...

Homework Statement A copper sheet of thickness 2.37mm is bonded to a Aluminum sheet of thickness 1.29mm. The outside surface of the copper sheet is held at a temperature of 100.0°C and the Aluminum sheet at 24.5°C. a) Determine the temperature of the copper-aluminum interface. b) How much...

Homework Statement An ice cube at 0.00 °C measures 14.9 cm on a side. It sits on top of a copper block with a square cross section 14.9 cm on a side and a height of 18.1 cm. The bottom of the copper block is in thermal contact with a large pool of water at 92.5 °C. How long does it take the...

Hi, I'm doing a group investigation on external wall insulation for my school building. The walls do not have a cavity and thus it has been proposed to put insulation over the exterior render of the wall. This is a fairly common building procedure. However, my task is to investigate the...

Homework Statement In a domestic heating system, a room is warmed by a 'radiator' through which water passes at a rate of 0.12kg s-1. The steady-state difference between the inlet and outlet temperatures of the water is 6.0 K. The radiator is made of iron of thermal conductivity 80 W...

1. I would like to test myself on how well I know my information about certain metals, some of them get me a bit puzzled. How would you rate the electrical conductivity of cast iron? Poor, good, excellent or best? Also the thermal conductivity of 304 stainless steel? Poor, good, excellent or...

I would like to test myself on how well I know my information about certain metals, some of them get me a bit puzzled. How would you rate the electrical conductivity of cast iron? Poor, good, excellent or best? Also the thermal conductivity of 304 stainless steel? Poor, good, excellent...

For a nonmetal what determines thermal conductivity is the propagation of lattice vibrations. As T increases these lattice vibrations collide with each other more often. Does this mean that the thermal conductivity will de- or increase?

If thermal resistance is additive, then how can the thermal conductivity of two (or more) materials be combined? Can it? Eg. a wall filled with straw and air, a hollow brick, a mixture of polystyrene and fibreglass wool (just some random ideas off the top of my head).

Hello, i'm doing my prep for my lab experiment tomorrow and have a few questions about the experiment. The schematic is attached. My lab script says the following; 2 questions. It says the precise rate of flow of water through the heat exchanger is unnecessary to know. Is this...

I'm not sure I fully understand the difference between thermal conductivity and thermal diffusivity as thermal properties of a material and would appreciate if anyone could clarify. I understand thermal diffusivity is for a transient case and conductivity is for steady state. This is what...

Hi, I'm hoping to achieve some intuition regarding the real and imaginary parts of the complex conductivity. The rule of thumb seems to be that the real part is due to the absorptive/dissipative processes and the imaginary part absorbs no work (over a time average). However, I feel like...

I am trying to devise a way to test the electrical conductivity/resistivity of the atmosphere through rising altitudes. The platform for the experiment is a NASA weather balloon with the allowance of a 1 kg payload. I have started by creating a sort of leaky capacitor design which involves the...

Hi, I was hoping someone could enlighten me on the thermal conductivity of air. I'm aware the λ for air is 0.024. Meaning its a very good insulating material. Much better than the conventional insulating material we use for conventional buildings such as EPS and XPS which are at λ 0.030...

How can I determine the thermal conductivity of two different aerial coolers' tubes, taking into account the ambient temperature of the air? The overall goal is to determine which cooler is able to cool water the best, but the data was taken during different outside air temperatures. Below...

What is the metal conductivity at ultraviolet frequency?

I use RTV silicone rubber to make moulds for hard candy. Hard candy is basically boiled sugar that is poured into moulds at just under 300 degrees F. The castings of hard candy develop bubbles on the surface because the silicone does not dissipate the heat, unlike traditional metal moulds...

Hi everyone, I am trying to find the mean free time between collisions for free electrons in a copper wire given the dimensions of the wire and the resistance, electron density and temperature. I figured I needed to find the conductivity, plug that into an expression for mean free path...

I am new to this field of electrical measurements and my question may sound amateurish but your suggestions will be highly appreciated. I have got a micron thick polymer sample with some kind of irregular shape. I mean with each sample the shape is being changed little bit as the shape is not...

Homework Statement One end of a metal rod is maintained at 100°C, and the other end is placed in a large container with ice and water at 0°C. The rod has length 50 cm and a cross-sectional area of 0.8 cm 2 . The heat conducted by the rod melts 4 g of ice in 5 minutes. Calculate the...

Homework Statement Hi there I am doing a mine engineering degree by correspondence. The lecture notes that I have calculating seepage and velocity etc is not very helpful and other then discussing darcys law and other concepts does not go through the formulas. My lecturer has gone on...

Hey all, i'm trying to set up a thermal model of a permanent magnet synchronous electric motor. This by doing a lumped system analysis of the motor. In the thermal network that I've set up, I'm trying to introduce an equivalent thermal conductivity value (W/mK) for the copper conductors plus...

What is the conductivity of metals at 0 kelvin? i think it will be zero because at 0 k entropy is zero. Every motion is cease.

Does anyone know where I can find a table of molar conductivities by element? I want to find the molar conductivity of sodium and chloride specifically. Thanks.

Relative motion between a permanent magnet and a conductor wire produces electric current in the wire. Would induced electric current be greater in a wire made of "magnetic" material like iron, "non-magnetic" material like copper, or it doesn't matter? In other words, is there relation between...

Homework Statement A hot reservoir is maintained at a temperature of 78 oC, and a cold reservoir is maintained at a temperature of 5oC. They are separated by 11.00 cm, and are connected by a cylindrical bar made of two materials. The radius of the bar is 0.83 cm. The upper part of the bar is...

What I know is Molar conductivity is The conductivity of the elctrolyte divided by its concentration . Can someone please explain the physical significance of this ? Also ionic conductivity depends on concentration, if I dilute the electrolyte the ionic conductivity decreases but Molar...

Homework Statement The conductivity of a material depends on a) Resistance(R) b) Area of cross section(A) c) Length(L) d) Resistivity(ρ) Homework Equations The Attempt at a Solution The formula for Resistivity is given by ρ = AR/L and Conductivity(σ) being the reciprocal of...

1. Hi, basically I'm trying to find an equation to find ion specific molar conductivity of salt water flowing between electrodes. Homework Equations resistivity: rho = RA/L conductivity: kappa = 1/rho conducitivity per unit concentration: lambda = conductivity/concentration this is ion...

Homework Statement This was determined from an experiment,where the resistance of 0.02M of KCl was to be determined [KCl]=0.02M conductance=2.86ms L=0.002768ohm^-1 to obtain k Co(NH3)4CO3]NO3 : conductance: 1.923ms concentration of cobalt complex: 0.002M Homework Equations k=RL...

Hi to everyone I'm working on mu thesis with this title: Calculation of graphene conductivity in the semiclassical regime And also I should calculate it with Boltzmann equation Is there anybody who can guide me for where to start and even how to calculate the graphene conductivity using...

Hi everyone. I was wondering if there is a convention for solving heat conduction problems. Specifically should one account for thermal expansion? The SI units for thermal conductivity are W/m/K. Does m include thermal strains already? It seems for basic problems it would be easier to...

I want to understand the conductivity of ZnO. I know it is non-linear (that's why it is used in surge arrester to begin with), but can anyone enlighten me on why it is non-linear? Is it the function of electric field, current, or anything? I'd appreciate if you can provide the expression of...

As I know, electrical conductivity is a second rank tensor. So in a cubic structure, there is no orientation dependence of electrical conductivity (isotropic). But how come Si has higher electron conducitivity along [001] and hole conductivity along [110]?

Landau's book defines it as thermal conductivity/density/specific heat at constant pressure while Chandrasekhar's book defines it as thermal conductivity/density/specific heat at constant volume. I am confused. Any comments?

Hey guys, I'm hoping someone can help me out, as i have an exam tomorrow and have no began panicing as I've found a question i can't seem to get to the end of... Here is the question itself; A large crucible contains a metal of thermal conductivity, κ = 12.5 Watts. m-1.K-1, electrical...

Hi, i'm searching for a material with the following properties: - high stiffness - low thermal conductivity - temperature resistance up to 150°C (not getting too soft at 150°C) - no low friction coefficient (so no PTFE) - good fracture behaviour (so no glass, ceramic) - cheap I've...

Hey, Assume I have a very large tank of some liquid with uniform but medium conductivity. I now insert two fine wires into the tank some distance (D) apart, and create an electrical potential difference between them (V). 1) If I were to take my voltmeter (input impedance very high, so we...

this isn't really a problem, I'm trying to understand the table in this link: http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-36.html basically it shows a wall assembly, it's 70 degrees on the inside, and it gives a list of the materials and their thicknesses in the wall if...

Homework Statement The brick wall of a building has dimensions of 4m by 10m, it is 15cm thick with a coefficient of thermal conductivity of 0.8 (Wm^-1C^-1). (a) How much heat flows through the wall in a 12-hour period when the average inside temperature is 20 C and the average outside...

Hi all, I am new to matlab, and I have a question (in page 2 and 3 of attached file). As I understand, i have some equations to calculate the thermal conductivity of the pipe-like solid, and I have to use Matlab to make a program to do it. But i don't know where to start? It may be easy...