## permeability

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permeability
1. (hydraulic conductivity) In general, the ability of a rock, sediment, or soil to permit fluids to flow through it. More precisely, the hydraulic conductivity is the volume flow rate of water through a unit cross-sectional area of a porous medium under the influence of a hydraulic gradient of unity, at a specified temperature. It is measured in units of m/s or m/day and varies with temperature. Typical values range from 10−6 m/day for clay to 103 m/day for coarse gravel. The magnitude of hydraulic conductivity depends on the properties of both the fluid and the medium. An alternative measure, used in the oil industry, is intrinsic permeability, measured in m2 (or in industrial units called darcies), which depends on the properties of the rock alone.

2. Property of a membrane or other barrier, being the ease with which a substance will diffuse or pass across it.

3. Capacity of a material to transmit fluids, expressed as hydraulic conductivity. In soils, the ease with which gases, liquids, or plant roots penetrate into or pass through a layer of soil.

4. (magnetic permeability) The ratio of the magnetic flux density in a medium to the magnetizing force. In free space (i.e. air) this is a constant, μ0 equal to 4π × 10−7.

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per·me·a·bil·i·ty / ˌpərmēəˈbilitē/ • n. 1. the state or quality of a material or membrane that causes it to allow liquids or gases to pass through it. 2. Physics a quantity measuring the influence of a substance on the magnetic flux in the region it occupies.

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permeability (symbol μ) In physics, ratio of the magnetic flux density in a body to the external magnetic field inducing it. This means a magnetic field is related to, and altered by, the presence of a substance it surrounds. The permeability of free space is called the magnetic constant (symbol μ0), and has the value 4π × 10−7 henry per metre. The relative permeability of a substance (symbol μr) is the ratio of its permeability to the magnetic constant.

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permeability
1. A property of a membrane or other barrier, being the ease with which a substance will diffuse or pass across it.

2. The capacity of a material to transmit fluids, expressed as hydraulic conductivity. This is the volume flow rate of water through a unit cross-sectional area of a porous medium under the influence of a hydraulic gradient of unity, at a specified temperature; it is measured in units of m/s or m/day and varies with temperature. Typical values range from 10−6 m/day for clay to 103 m/day for coarse gravel. In soils, the ease with which gases, liquids, or plant roots penetrate into or pass through a layer of soil.

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permeability
1.. A property of a membrane or other barrier, being the ease with which a substance will diffuse or pass across it.

2.. The capacity of a material to transmit fluids, expressed as hydraulic conductivity. In soils, the ease with which gases, liquids, or plant roots penetrate into or pass through a layer of soil.

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permeability (per-mi-ă-bil-iti) n. the ability of membranes to allow soluble substances to pass through them. See also semipermeable membrane.