# What is Permeability: Definition and 126 Discussions

Permeability in fluid mechanics and the Earth sciences (commonly symbolized as k) is a measure of the ability of a porous material (often, a rock or an unconsolidated material) to allow fluids to pass through it.
The permeability of a medium is related to the porosity, but also to the shapes of the pores in the medium and their level of connectedness. Fluid flows can be influenced in different lithological settings by brittle deformation of rocks in fault zones; the mechanisms by which this occurs are the subject of fault zone hydrogeology.

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1. ### Do Magnetic properties change?

Hi Quick question related to magnetism If I have a magnetic core and place that core onto a magnet, then roll the core on a flat surface ( whilst its still on the magnet), does that increase the permeability and magnetic field of that core ? If so, what is the theory behind that. thank you in...
2. ### Cylindrical Permeability Problem: Help on how to set up

I was asked to give an estimate for a three dimensional permeate problem and I need an assist in how to setup a model equation. Picture a 6" underground cylindrical bore. The depth of the cylindrical bore is 150 feet. The bore is sealed at the bottom and the permeability below the bore bottom...
3. ### How to Factor Vapor Retarders into Relative Humidity & thus Mold Risk

Relative humidity can be calculated if you know dewpoint and temperature - by formulae such as the August-Roche-Magnus approximation. All methods - all formulae - ignore vapor resistance (perms). Surely scientists/engineers have a way to then, as a subsequent step, bring vapor retarders into...
4. ### Permeability of Iron: How Does It Affect Electromagnets?

I know that iron is typically used in electromagnets to create a stronger magnetic field. But what is the exact nature in which that happens? When it goes in is it slowed down at all while traveling through the metal or does it still keep going at the speed of causality? Also does it have the...
5. ### I Are permittivity and permeability quantities that can be predicted?

For example, can you predict the permittivity and permeability of a substance if you know what the atomic composition is? Is it a stat mech problem?
6. ### Ampere's Law for a toroid (finding relative permeability of iron)

Why is this equation: B(D - d)/mu + Bd = mu0 N I true? B = magnetic field in the hole of the toroid D = Average diameter of the toroid d = Diameter of hole of toroid mu = relative permeability of iron, or whatever the toroid is made of mu0 = 4pi x 10^-7 N = Number of turns on the toroid I =...
7. ### Magnetic permeability and optical impedance

Hi, It's given that an electromagnetic wave (5.10^14 Hz) traveling in an environment with the index n = 1,33, where the magnetic permeability (μ) is equal to the magnetic permeability in a vacuum (μ0). The optical impedance (Z) is given by the formula : Z = μ . c/n. I tried to turn μ into μ0 to...
8. ### Magnetic Permeability: Temperature Effects

One more thing i forgot to add, is magnetic permeability of a metal constant irrespective of its temperature including superconducting temperature ?
9. ### Magnetic Field, Field Intensity and Magnetisation

Hello there, I've worked through this problem and I would just like to check whether I've understood it correctly. I found ##\vec H##, ##\vec B## and ##\vec M## using Ampere's Law and the above relations as I would for any thin current carrying wire and these were my answers: \vec H = \frac I...
10. ### Can you calculate optical density from permittivity and permeability?

Does electric perm and magnetic perm give you enough info to work out OD? Thanks in advance
11. ### B Planck-like values out of permeability and permittivity

What happens if we make a dimensional analysis of permeability and permittivity ? Will we get a minimum possible amount of electric and magnetic values?
12. ### Efficiency of heating up aluminum vs steel by induction

Summary: In a heating by induction experiment performed, the idea was to determine the efficiency of heating up a small steel cylinder, an aluminum cylinder and then compare the two efficiencies. The cylinder was surrounded by a metall coil that alternating current was going through...
13. ### Permeability of copper in the microwave frequency range

Relative DC permeability of copper is 1. Conductors are considered dispersive and therefore the permeability should change with frequency. Where can I find data or how can I calculate permeability of copper in Ghz frequency range?
14. ### Rigid high magnetic permeability materials

Hi, for lower frequencies most electrical devices use laminated electric steel , like transformers and motors. But this makes the core made up of individual metal sheets and in older transformers taking the core apart sometimes results in the individual sheets falling apart. Is there any...
15. ### I What was the value of the permeability constant in 1865?

What is the value of the permeability constant in 1865, the time when Maxwell's theory was first published? What was the experimental method used to determine the constant. Who did the experiment.
16. ### Automotive Hydrogen Car Fuel Tank: Preventing Permeation & Valve Check

How do hydrogen powered cars prevent the permeation of hydrogen through the valve used to fill the car's tank with hydrogen? Is a regular check valve used or is the valve special in some way?
17. ### I Relative Permitivity, Permeability & Refractive Index of Water

How does the relative permitivity and relative permeability related to the refractive index of a dielectic medium like water?
18. ### Gas pressure differentials and permeability

We are trying to design a new product which uses gas pressures in various ways. We are a little foxed about partial pressures: Imagine a small cylinder; 6in long + 1in in diameter. The cylinder is made from steel. The cylinder is divided into two equal compartments – A and B. Each compartment...
19. ### How does stacking and creating an air gap affect fabric air permeability?

I have a fabric from a windshirt testing at 40 CFM under ASTM D 737 (125 Pa). I am interested in understanding what would happen to air velocity if two layers were stacked and tested. Next, how would the results be affected by an air gap between the two layers?
20. ### Why we use relative permeability

Why we use relative permeability if we have absolute permeability in electromagnetism?
21. T

### Magnetic flux and inductance?

If a current flows in a straight wire, a certain amount of magnetic flux will be generated around it. Now suppose I put an iron tube around the wire (but don't change the current). I know the inductance will increase, but is that because more total flux is now being generated, or is the total...
22. ### I Meaning of permeability in free space

Permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. And the inductance of an electric circuit is one henry (H) when an electric current that is changing at one ampere per second results in an electromotive force of one volt across...
23. ### Electric Permittivity, Magnetic Permeability & Suceptibility

Can anyone please explain me the physical significance of these concepts?? Electric permittivity, Magnetic Permeability & suceptibility
24. ### B Permittivity and Permeability changes

I have a question about permeability and permittivity of free space. Theoretically speaking. If either one or both were to increase in value would that make the speed of light be faster or slower. I know they are constants. I am just curious if they did change what would happen.
25. ### 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...
26. ### Uncertainty analysis of 2 port measurement

I analyzed uncertainty analysis of 2 port measurement. I referenced 2 book "Transmission Reflection and Short Circuit Line Methods for Measuring Permittivity and Permeability" at pages 31 equation(2.83) "Transmission and Reflection and SCL Permittivity Measurements" at pages 44 equation(2.67)...
27. ### A Diffusion of Hydrogen through Molybdenum alloy

I have been preforming experiments to study the diffusion of Hydrogen through Molybdenum. According to Sievert's law diatomic molecules would diffuse as atoms. But according to my experiments I notice that the flux of hydrogen is directly proportional to the pressure of hydrogen and not to the...
28. ### Need help with permeability of free space.

Homework Statement In a lab that I did in Physics we calculated the magnetic field of a solenoid while constantly increasing the number of time the wire was wrapped around the electromagnet. After I obtained all the values, plotted it in a graph and found the line of best fit, the slope came...
29. ### B Does gravity change the permittivity/ permeability of vacuum?

For example if you send a light beam towards a massive object the propagation speed will reduce if μ and ε are increasing, but the spacetime curvature will compensate for that reduction.
30. ### I Inhibit repulsion between two like poles

Please excuse the lay terms that will follow. I have been doing some reading on "magnetic shielding" and have come across alloys such as MuMetal which have high permeability and so can block interaction between two magnets. My question; Is this inhibition of interaction between the two...
31. ### I Does Free Space Permeability Change with Applied Magnetic Fields?

In free space does permeability increase or decrease when a magnetic field is applied?
32. ### Iron & Magnetic Fields: Permeability or Screening?

Hi All, It is said that iron has a high "permeability" for the magnetic field, it let's the magnetic field pass through it more easily. But it is also said that iron screens the magnetic field? Don't these two contradict themselves? Thanks, Ionel
33. ### How Does an Electromagnetic Wave Propagate in Glass?

Homework Statement A harmonic EM-wave is propagating in glass in the +x-direction. The refractive index of the glass ##n = 1.4##. The wave number of the wave ##k = 30 \ rad/m##. The magnetic portion of the wave is parallel to the y-axis and its amplitude ##H_0 = 0.10A/m##. At ##t=0## and ##x =...
34. ### Viscosity -- capillary radius, and permeability threshold

In a demonstration of the qualities of liquid Helium in type 1, and type 2 the fact that a super-fluid can permeate through capillaries which are too small for type 1 Helium to pass through. I was wondering about the equation which determines the capillary radius threshold under which the...
35. ### Find the magnetic permeability of the iron bar.

Homework Statement In a solenoid with 12 enamels for cm passes the current 2 A. Find the magnetic permeability of the iron bar inside it.(B0=1.508 T) Homework Equations B=μ0*I*N/l(length) The Attempt at a Solution We have N/l(length)=1200 enamels/meter B=4*10^-7*3.14*25*1200=0.003T Now...
36. ### B Derive Vacuum permeability and permeability....

Derive Vacuum permittivity and permeability using Quantum Field theory or String theory! If QFT or String theory is real fundamental theory, it can be derived the permittivity and permeability of vacuum. << Moderator's note: personal contact details deleted>>
37. ### Magnetic permeability Vs. Magnetic susceptibility

Hi I'm trying to find the difference between magnetic susceptibility and permeability? Do they both mean the same thing? If not, can anyone clear things up for me?
38. ### Dynamic Relative magnetic permeability

I want to know that are there any materials or methods by which their relative magnetic permeability (μr) be instantaneously,continuously & periodically varied. Kindly provide the reference document/video for the description if possible.
39. ### Who Derived the Value of Magnetic Permeability in a Classical Vacuum?

Who is credited for deriving the value of magnetic permeabilty in a classical vacuum? How would one go about sourcing information in relation to such a value?
40. ### What is the behavior of magnetic saturation in 2-D?

Dear all, I have a question about magnetic saturation and I can't find any sources addressing my questions. I am relatively familiar with magnetic saturation and that the relative permeability of highly saturated iron becomes rather small. There are numerous sources with figures showing...
41. ### Understanding Magnetic Permeability

As per some websites that I visited, "Magnetic Permeability is the ability of a material to support the formation of a magnetic field" so in materials with higher permeability the magnetic fields should be denser that materials with lower permeability. Lets say we have a magnetic circuit with a...
42. ### Does classical vacuum permittivity have a QM analog?

According to Maxwell's Equations, the classical vacuum permittivity and permeability have a very important role: They determine the speed of light. But it seems like these two important concepts are not as precisely defined in the quantum world. Are there rigorous analogs of these two...
43. ### Electromagnetism: Magnetic Field, change in permeability

Hello everyone. I've built a Helmholtz coil and I'm attempting to understand how the magnetic field direction and magnitude will be effected do to a material with a particular permeability. In the first picture I have an infinitely long cylinder with a particular thickness and permeability...
44. ### How Does Increasing Core Permeability Affect an RL Circuit's Performance?

In an RC dc circuit at steady state, if the permitivitty of the capacitor is increased by inserting a different dielectric, additional charging current will flow and the capacitor will accept more charge (due to increase in capacitance). What will happen if the inductance in an RL circuit is...
45. ### Permeability in ferromagnetic material (AC)

Homework Statement The following coil-wound core (core length = L , Gap length = lg, cross- sectional area = A , core permeability = only hysteresis graph is given, N = N turns) is driven by a Voltage source, is known that the current in the coil is 60hz AC. Determine...
46. ### Viscosity, No Slip, Permeable Couette plate

I am trying to understand the no slip condition (parallel velocity =0) in the presence of a permeable surface (in this case a Reverse Osmosis filter mesh ). Does the presence of permeability affect the no slip condition ? Intuitively For a gas Where viscous effects are dominated by momentum...
47. ### Magnetic Moment and permeablity

Hi, I understand that magnetic flux is like electric current and will take the path of least resistance, but I really don't like the current analogy and here's one question where it doesn't help: Say you've got a piece of Ferro Iron where the magnetic moments are not lined up, you put a...
48. ### Looking for what I thought would be a simple Permeability Q

Hi, I've been thinking about how to calculate a permeability curve, I thought this would be an easy to find online but unfortunately I haven't had any luck. From what I can graphically see below: It appears to me that mu for a ferromagnetic material is proportional to the derivative of B vs H...
49. ### Fluids - Darcy's Law, permeability of a filter

Homework Statement Derive an analytical expression for the permeability (k) of the structured porous medium (which is a size selective filter) constituted by a periodic array of cylinders of diamter d separated by a distance h = 1.8d Homework Equations Q=k*(μ/A)*(Δp/L) Q = volumetric flow rate...
50. ### Calculate the required relative permeability of magnetic mat

Homework Statement Consider the core of dimensions given in example 5-1. A coil requires an inductance of 23.6μH, a maximum current of 4A is allowed, and flux density is not to exceed 1.3T. Calculate the required relative permeability, μr, of the magnetic material that should be used. (HINT...