Small Field

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Small Field

• TMF 2004
• Gymnasium Eliky Krásnohorské

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Magnetic needle

• magnetic needle indicate direction of magnetic
  field vector
• ideal needle is movable in all directions
• measuring vertical and horizontal part, then
  calculation resultant

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Measuring magnetic induction

• direct force measuring is not ideal
• using secondary field
• constant field, measuring angle size
• constant angle, variable magnetic field

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Secondary field generators

• generated field must be homogenous
• solenoids arent right we cannt direct see
  deflection of needle
• preferable are Helmholtz coils with adequate
  dimensions

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Used Helmholtz coils
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Scheme of Helmholtz coils
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Equation

• Bx - magnetic induction
• n - count of turns
• r - radius of coils
• d - distance of coils
• I leak curent
• ? - absolute permeability

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Numeric calculation

• Bx - magnetic induction
• n - count of turns (10)
• r - radius of coils (0,1 m)
• d - distance of coils (0, 14 m)
• I leak current (0,404 A)
• ? - absolute permeability (1,257.10-6 H.m-1)

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Result

• measured horizontal part of magnetic induction is
  27,92 µT
• general value for middle Europe is 20,26 µT
• vertical part wasnt measured (we didnt have a
  vertical magnetic needle) but in the middle
  Eurepa is important

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Other methods for measuring small magnetic fields

• proton precission magnetometers
• optically pumped magnetometers
• overhauser magnetometers
• fluxgate magnetometers