What is Conductance: Definition and 64 Discussions

The conductance quantum, denoted by the symbol G0, is the quantized unit of electrical conductance. It is defined by the elementary charge e and Planck constant h as:








{\displaystyle G_{0}={\frac {2e^{2}}{h}}}
= 7.748091729...×10−5 S.It appears when measuring the conductance of a quantum point contact, and, more generally, is a key component of the Landauer formula, which relates the electrical conductance of a quantum conductor to its quantum properties. It is twice the reciprocal of the von Klitzing constant (2/RK).
Note that the conductance quantum does not mean that the conductance of any system must be an integer multiple of G0. Instead, it describes the conductance of two quantum channels (one channel for spin up and one channel for spin down) if the probability for transmitting an electron that enters the channel is unity, i.e. if transport through the channel is ballistic. If the transmission probability is less than unity, then the conductance of the channel is less than G0. The total conductance of a system is equal to the sum of the conductances of all the parallel quantum channels that make up the system.

View More On Wikipedia.org
  1. Olha

    A From Nyquist plot to real conductivity spectra (sigma)

    Hi, I have data of impedance but due to limitation of software after measurement I do not receive numerical values for admittance and real conductivity vs frequency. How mathematically I can convert Nyquist plot into plot real conductivity vs frequency?
  2. A

    Compare the conductance of an insoluble salt with soluble one

    Options (a) and (b) are facts and therefore correct. Since ionic bonds weaken with temperature, ionic mobilities should increase with temperature. Also in physics, we learnt that the resistance of every material other than conductors (i.e. semi-conductors, insulators and electrolytes decreases...
  3. nafisanazlee

    Chemistry A confusion about conductance of weak electrolytes

    My attempt is the handwritten one. But my reference book solved it in a different way, they left a note saying at infinite dilution α = 1(100%). (the attached picture) Which one is the correct approach?
  4. soothsayer

    Gas conductance through tube at low pressure

    I have a vacuum chamber of volume V connected to a vacuum pump via a tube of radius R and length L, and I want to design this "tube" such that R can be controlled in order to provide a constant rate of pressure change inside of the chamber of 2.5 mbar/sec, from atmosphere down to ~0.5mbar...
  5. B

    I Energy Modes affect on Conductance (N-P-Superconductor layers)

    I am considering a system that includes a pn-region with N first then P, then a superconductor, but I am not interesting in the effect of the modes present due to the confinement of the p-region of the system on the conductance (from electrons to holes). How do negate these energy modes in the...
  6. Q

    A Conductance of an interacting quasi one dimensional wire

    Assuming the electrons are non interacting and spin degenerate, the conductance of a quasi one dimensional quantum wire is quantised in units of 2e^2/h. For small voltages, we simply count how many bands have their bottoms below the chemical potential and multiply this by 2e^2/h. This is due to...
  7. Dr-LucienSanchez

    Calculate the total resistance by integration using the conductivity equation

    (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...
  8. F

    How does a digital multimeter measure conductance?

    Preface to thread: Back in October I created a thread titled "How does a digital ammeter work?" That thread was about how digital ammeters measure current. The purpose of this thread is to learn how digital multimeters measure conductance, not voltage. This is a separate issue for 2 reasons...
  9. tworitdash

    Relation between conductance and dielectric relaxation time

    I am studying about dielectric materials and their relaxation properties. There are several ranges of electromagnetic frequencies where different material show different kinds of resonance starting from molecular to atomic motions. Based on the frequency dependence of the imaginary part of the...
  10. chandrahas

    B Confused about the Drude model

    I was thinking about hall conductivity, when this question popped up. If there is a magnetic field and an electric field perpendicular to it, then a hall current is generated since the ions have larger gyro radii compared to electrons. Now this current would produce a J cross B force in the...
  11. DeathbyGreen

    I Understanding AC and Optical Conductivity: Conflicting Information Clarified

    Maybe someone can help me out; I've been seeing conflicting information on the meaning behind optical conductivity vs AC conductivity. Some papers seem to post plots of transmission and reflectivity, and others a Drude-like \sigma(\omega). In many textbooks I can't seem to find a satisfactory...
  12. J

    A Interference in electron conductance through e.g. molecule?

    Imagine attaching electrodes to a complex sample, e.g. a semi-conductor or a single chemical molecule, leading to some electric current. Can we decompose this electron flow into local flows? - like locally attaching amperometer and counting what fraction of electrons flow directly between given...
  13. hackhard

    Resistance from fingertip to Earth wire

    i connected one probe of digital mutimeter to the Earth terminal of domestic ac supply and held the other probe. it showed resistance of 1.8Mohm . but when i touched that end (one i'd held) to the floor. it displays 1( beyond 200Mohm ). why so ? shouldn't resistance be lesser?doesnt any current...
  14. M

    Theory/construction of conductance measuring device (films)?

    Hi, So I have this situation, I'm totally inexperienced with anything electricity. But as faith has it sometimes, suddenly I need a device that would be able to measure the electrical conductivity of a thin film. Is there anyone who could guide me what would be the essential parts of a system...
  15. M

    A Boundary Conductance in nanomaterials

    Greetings, I hope this is the right place to ask. I have been working with modeling of thermal conductance, G [W/K] of semi-conductor nanowires as a function of temperature. To start, thermal conductivity of a nanowire is modeled using BTE (Boltzmann Transport Equation). Then the conductance...
  16. kostoglotov

    How conductors/resistors affect electric fields?

    Disclaimer: I'm not sure if this is the correct forum. An ideal conductor (ideal = no resistance) is essentially taking the electric field at one terminal and connecting it to the other terminal. Charge moves when it is in an electric field, electric field strength is in Volts per meter, or...
  17. electric jake

    Electrical Resistance or Conductance of Carbon Dioxide

    I wanted to do a science experiment and it is very important that i learn the electrical resistance of carbon dioxide. From what i would guess, this may be wrong, but carbon dioxide and the atmosphere on Earth probably have a similar electric resistance due to the fact carbon dioxide already...
  18. Rushikesh Sarda

    Are density and resistivity proportional?

    Today while reading a book i read that conductance of a metal depends on its density. But it is also dependent on its resistivity. Does that mean that resistivity and conductivity are proportional to each other?
  19. S

    Conductance of heat through concrete

    Homework Statement In an electrically heated home, the temperature of the ground in contact with a concrete basement wall is 10.7 oC. The temperature at the inside surface of the wall is 21.4 oC. The wall is 0.17 m thick and has an area of 6.4 m2. Assume that one kilowatt hour of electrical...
  20. A

    Relation between Specific Conductance and Equivalent Conductance

    I have a question about the derivation of the formula for relation between Specific Conductance and Equivalent Conductance i.e. Eq. Conductance = k.V where, k= Specific Conductance ,V=Volume in ml Given link explains the derivation...
  21. C

    Calculating Thermal Conductance of Axial Cylinder

    How to calculate the thermal conductance ( in axial direction ) of a cylinder having length equal to its radius
  22. W

    Why is the conductance quantized?

    according to the Landauer formula, the conductance is proportional to the transmission probability. But the transmission probability is not quantized generally So why is the conductance quantized?
  23. T

    How can I calculate skin conductance from voltage readings in my research study?

    I am collecting skin conductance data for a research study. For this, we apply a constant voltage (5v) to a participants finger and then measure the voltage at another finger (or I think this is what is happening, there is also something about a resistor in there [see attached schematic])...
  24. A

    Relationship Between Conductance and the Dielectric Constant

    Hello all, I'm new to the forum so I hope I'm posting this in the correct section. I'm currently conducting an experiment in which I'm examining how the dielectric constant of a binary mixture changes with concentration and temperature using a parallel plate capacitor for measurements. The...
  25. Arkavo

    Conductance of 2 bodies: Is it dependent on geometry?

    Homework Statement I have 2 arbitrarily shaped conductors with charge Q1 and Q2 with potetials V1 and V2 respectively. I then short them (connect with a thin metallic thread) now i have to prove that the amount of charge that flows from one to the other is: Only dependent on the geometry of...
  26. RabbitWho

    Poligraph tests test resistance or conductance?

    Homework Statement Question: "What does a polygraph test measure; skin resistance or conductance?" To me this is two sides of the same coin and it seems it must be measuring both. Homework Equations The Attempt at a Solution I thought that the person is acting as a resistor so I wrote down...
  27. S

    Shubnikov de haas oscillations, conductance quantization

    Hi all I'm just studying the QHE and Shubnikov de Haas oscillations. There are two points I find somehow confusing: 1. If you look at ρxx (resistance along the direction of applied field), you will find oscillations of this resistance as a function of the external magnetic field. Whenever...
  28. X

    Thermal Conductance Through Two Materials

    I had a thermal conductance homework problem where heat flowed through gold, and then silver. Both materials were of the same length and same cross sectional area. The problem mentioned that the energy transfer had reached a steady state, and I found through doing the problem that under these...
  29. A

    A2 Physics Experiment: Electrical Conductance Through Salt Solution

    After summer I have to do my physics A2 experiment coursework. I really like working with electricity and looking at what happens at an atomic level, but I fear that what I want too do is more chemistry than physics. I had the idea of look at electrical conductance through a salt solution...
  30. L

    Conductance, gas flow and pressure question

    Hi there, I have been doing some research about vacuum system setup and I've seen the setup shown in the attachment. Pressure: P1a, P1b, P2a, P2b Throughput/gas flow: Q1, Qs Pump speed: Sp (pumping speed of the pump) Conductance:Ca, Cb, C Some papers have assumed that P2a = P2b, but...
  31. Femme_physics

    Transistor at cutoff, conductance, or saturation?

    Hi everyone, took a bit of a break lately...but with 6 days left to the final test of electronics, I figured I'd clear up some understandings I have Homework Statement http://img225.imageshack.us/img225/4474/vbbreversed.jpg I'm asked if the VBB potentials are flipped, at what condition will...
  32. P

    Conductance per unit length of a co-axial cable (Intro to Electromagnetics)

    Homework Statement Starting with: G = \frac{I}{V}= \frac{-\int_{s}\sigma\mathbf{E}\cdot d\boldsymbol{s}}{-\int_{l}\boldsymbol{E}\cdot d\boldsymbol{l}} Derive the conductance per unit length, G', of a coaxial cable by assuming a line charge of \rho_{l} on the center conductor...
  33. W

    Carbon Nanotube FET: Gate Voltage and Conductance

    i don't understand how an applied Voltage on a (intrinsic) Carbon Nanotube could change its conductance... There is not a population inversion like in mosfet. So, which is the physics? Where this carriers can from? thank you.
  34. N

    Mutual Conductance formula/computation in transmission line

    Hi all, I am trying to compute the coupling effects or crosstalk in the circuit attached. In MTL (multiconductor transmission line) model of two wire or three wire lines for main lines, how to calculate or simple equation of mutual conductance? which is denoted as g12 in the circuit...
  35. C

    What's the inverse of conductance?

    I'm doing an experiment today in class and I just wanted to know what's the inverse of conductance (expressed in S) and its units in the SI system. Thanks for viewing!
  36. H

    Quantised Conductance - Doped Carbon Nanotubes

    As I understand it, carbon nanotube (CNT) exhibits quantised conductance (2e^2/h) because the mean free path length of carbon nanotubes are often longer than the length of the tubes. If one is to substitutionally dope CNTs (say armchair metallic CNTs) with other atoms of similar size, for...
  37. P

    Leakage Conductance of Cylindrical Coax Cable

    Homework Statement Find the leakage conductance per meter of a cylindrical coax cable whose inner conductor (r1) is 0.125" (3.175*10^-3 m) and whose outer conductor (r2) = 0.5" (1.27*10^-2 m) if the space between them is filled with a material whose: \varepsilon_r = 2 and \sigma_c =...
  38. M

    Heat conductance and temp measurement

    Homework Statement i'm trying to find out how to model a system consisting of a body at a finite temperature, connected to a heat conducting rod that is lagged (see scanned image) and a thermometer (or any other temp measurement device), what would i take into account while modelling this...
  39. B

    Why is conductance used instead of resistance in circuits?

    Hello EE forum ! I would like to talk about conductance and resistance. I understand both terms. And formulas that they derived from. First newbie question: Each element has conductance and and resistance(admittance)? Probably yes, just checking. Second question: In process of...
  40. K

    Peltier heat conductance concept question (PID)

    Hey, I am making a cooling system using a peltier junction with a cold finger on one side and a heat sink on the other. For my heat sink, I am depositing the heat into the phase change of a bismuth alloy (about 70 deg C). When the current across the peltier is increased and the hot side...
  41. M

    Understanding Quantized Conductance in Nano-sized Objects

    In nano-sized objects ( at least one dimension < 100 nm) the conductance is quantized. It is given in multiples of G _0 = 2(e^2) / h . Now, that means that Ohm's law would look like I = GV, where G is an integer multiple of G_0. What does this actually mean however? How does this limit the...
  42. J

    DC conductance in the presence of a time-dependent electric field

    I calculated the DC conductance of a 2DES in the presence of a time-dependent (periodic) electric field using the Boltzmann equation some time ago, and I'd like to verify the results numerically. Ideally I'd like to perform a computation along the lines of a recursive Green's function...
  43. B

    How Thick Should the Air Layer Be to Limit Heat Loss in Winter Clothing?

    Homework Statement A man of 75 kg (1.77 m^2 surface area) in weight, dressed in appropriate winter clothing stands on a winter pond. The temperature outside is -5 degrees Celsius. Assume that the surface layer of his skin is 5 mm thicker and is not perfused with blood (behaves as an insulating...
  44. W

    Proton mobility vs. conductance in ice

    Greetings, I'm trying to understand how protons might move through solid water ice. More specifically this concerns how deuterium/hydrogen ratios are used to date ice core samples drilled into glaciers. On one hand I am told that, once it is deposited from the atmosphere in the form of...
  45. B

    A voltage divider in terms of a conductance

    I am looking at the following application note that goes into nodal analysis of op amps: http://www.maxim-ic.com/appnotes.cfm/an_pk/1939/ and down at the bottom where they're analyzing the Wien bridge oscillator the equation at the negative input of the op-amp taken from the output in terms of...
  46. B

    LDR: Why is conductance proportional to log(intensity)?

    I am doing a experimental report on various solid state devices and have come unstuck on my work with LDRs. I have data relating conductance of a CdS photo-resistor to intensity of (white) light. The problem is that I am completely unsure as to why there is a log relationship, as has been...
  47. C

    Why Is Quantum Contact Conductance Maximized at 2*q^2/h Even Without Scattering?

    My question is how the maximum quantum contact conductance 2*q^2/h comes from. The maximum contact conductance can only be obtained when there is no scattering in the contacts between nano-channel and two big pads. (To my understanding, resistance comes from scattering, but if there is no...
  48. D

    Calculating Resistance and Impedance in an Electric Circuit

    Homework Statement 123984[/ATTACH]"] Homework Equations H= (NI)/ (2(Pi)r) V=IR The Attempt at a Solution a) total resitance = 100ohms? from this would the current be 0.12A over 1ohm resistor: 0.12V not sure if this is correct even. Any help would be much appreciated.
  49. D

    Harvest Free Electrons from Plasma Field?

    hey, I have a question, it might be really stupid, but I'm probably not as smart as any of you here. Anyway: if you had a sustained plasma field held in place, maybe spinning in a toroidal motion, is it possible to "harvest" free electrons from the field by an anode, and feed it back into the...