Μαγνητική Διαπερατότητα
permeability, Μαγνητική επιδεκτικότητα


- Mία Φυσική Σταθερά
Ετυμολογία[]
Η ονομασία "Μαγνητική" σχετίζεται ετυμολογικά με την λέξη "Μαγνητισμός".
Εισαγωγή[]
In Ηλεκτροδυναμική, permeability is the degree of Μαγνήτιση (magnetization) of a material that responds linearly to an applied Μαγνητικό Πεδίο.
Magnetic permeability is represented by the Greek letter μ. The term was coined in September, 1885 by Oliver Heaviside.
In SI units, permeability is measured in henries per metre, or newtons per ampere squared. The constant value is known as the magnetic constant or the permeability of vacuum, and has the exact or defined value = 4π×10−7 N·A−2.
Relative permeability[]
Relative permeability, sometimes denoted by the symbol μr, is the ratio of the permeability of a specific medium to the permeability of free space μ0:
In terms of relative permeability, the magnetic susceptibility is:
χm, a dimensionless quantity, is sometimes called volumetric or bulk susceptibility, to distinguish it from χp (magnetic mass or specific susceptibility) and χM (molar or molar mass susceptibility).
Magnetic permeability & susceptibility for selected materials | |||
---|---|---|---|
Medium | Susceptibility | Permeability x10-6 | |
Mu-metal | 20,000 [1] | 25,000 N/A2 | at 0.002 T |
Permalloy | 8000 [1] | 10,000 N/A2 | at 0.002 T |
Transformer Σίδηρος (iron) with ρ=0.01 µΩ·m | 4000 [1] | 5000 N/A2 | at 0.002 T |
Χάλυβας (Steel) | 700 [1] | 875 N/A2 | at 0.002 T |
Νικέλιο (Nickel) | 100 [1] | 125 N/A2 | at 0.002 T |
soft ferrite with ρ=0.1 Ωm | source, ferroxcube | 5000 N/A2 | < 0.1 mT |
soft ferrite with ρ=10 Ωm | source, ferroxcube | 2500 N/A2 | < 0.1 mT |
Platinum | 2.65 × 10−4 | 1.2569701 N/A2 | |
Αργίλιο (Aluminum) | 2.22 × 10−5 [2] | 1.2566650 N/A2 | |
Hydrogen | 8 × 10−9 or 2.2 × 10−9 [2] |
1.2566371 N/A2 | |
Vacuum | 0 | 1.2566371 N/A2 | |
Sapphire | −2.1 × 10−7 | 1.2566368 N/A2 | |
Copper | −6.4 × 10−6 or −9.2 × 10−6 [2] |
1.2566290 N/A2 | |
Water | −8.0 × 10−6 | 1.2566270 N/A2 |
Permeability varies with magnetic field. Values shown above are approximate and valid only at the magnetic fields shown. Moreover, they are given for a zero frequency; in practice, the permeability is generally a function of the frequency. When frequency is considered the permeability can be complex, corresponding to the in phase and out of phase response.
Note that the magnetic permeability has an exact value in SI units (i.e. there is no error bar or uncertainty in its value), a fact that is intimately related to the next formula:
, and that the definition that the speed of light is exactly 299,792,458 meters/second.
Υποσημειώσεις[]
Εσωτερική Αρθρογραφία[]
Βιβλιογραφία[]
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Αν και θα βρείτε εξακριβωμένες πληροφορίες "Οι πληροφορίες αυτές μπορεί πρόσφατα Πρέπει να λάβετε υπ' όψη ότι Επίσης, |
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αν διαφωνείτε με όσα αναγράφονται σε αυτήν
- Όχι, στις διαφημίσεις που περιέχουν απαράδεκτο περιεχόμενο (άσεμνες εικόνες, ροζ αγγελίες κλπ.)