Electromagnetism - Find length of coil

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SUMMARY

The discussion revolves around calculating the length of an iron-free cylindrical coil with 9400 turns, a thickness of 0.6 cm, and an inductance of 68 mH. The relevant formula used is L = N² * μ₀ * μ_r * A / l, where μ₀ is the magnetic field constant (4π x 10⁻⁷ Wb/Am). The solution requires determining the cross-sectional area (A) of the wire and the relative permeability (μ_r), which is not provided but is implied to be favorable for calculations. The calculated length options presented are 63mm, 54mm, 46mm, and 36mm.

PREREQUISITES
  • Understanding of inductance and its formula.
  • Knowledge of magnetic field constants, specifically μ₀.
  • Ability to calculate the cross-sectional area of a circular wire.
  • Familiarity with relative permeability (μ_r) in electromagnetism.
NEXT STEPS
  • Research how to calculate the cross-sectional area of a circular wire.
  • Learn about relative permeability (μ_r) and its significance in coil design.
  • Study the implications of using different core materials in inductance calculations.
  • Explore the relationship between turns, inductance, and coil length in electromagnetic theory.
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Students studying electromagnetism, electrical engineers designing coils, and anyone involved in inductance calculations for practical applications.

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Homework Statement


Calculate the length l of an an iron-free cylindrical coil if it has 9400 turns (N), a thickness of 0.6cm and an inductance L = 68 mH. Take magnetic field constant \muo = 4\pi x 10-7 Wb/Am

(a) l = 63mm
(b) l = 54mm
(c) l = 46mm
(d) l = 36mm

Homework Equations



L = N2 \muo \mur A / l

The Attempt at a Solution



0.068 = (9400)2 x ( 4\pi x 10-7) \mur A / l

how to calculate if \mur and A are not given??
 
Last edited:
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Given that the core is iron-free, what sort of material would you expect to find there? This material has a very nice relative permeability for calculations!

If you have a (circular cross section of a) piece of wire that is 0.6cm thick (diameter), what is the (cross sectional) Area of this wire?

*NB: Beware of units, as 'l' is in meters, 'A' is in meters squared and 'L' is in Henry's.
 
Last edited:

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