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Small Field

This document discusses the principles and methodologies for measuring small magnetic fields using magnetic needles and Helmholtz coils. It explains how the magnetic needle indicates the direction of the magnetic field vector, the importance of measuring both vertical and horizontal components, and the fundamental equations for magnetic induction. Additionally, it compares different methods for measuring small magnetic fields, including proton precision magnetometers and fluxgate magnetometers. The results from a numeric calculation are included, providing insight into the magnetic induction values relevant to middle Europe.

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Small Field

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  1. Small Field TMF 2004 Gymnasium Elišky Krásnohorské

  2. 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

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

  4. Secondary field generators • generated field must be homogenous • solenoids aren´t right – we cann´t direct see deflection of needle • preferable are Helmholtz coils with adequate dimensions

  5. Used Helmholtz coils

  6. Scheme of Helmholtz coils

  7. Equation • Bx - magnetic induction • n - count of turns • r - radius of coils • d - distance of coils • I – leak curent •  - absolute permeability

  8. 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)

  9. Result • measured horizontal part of magnetic induction is 27,92 μT • general value for middle Europe is 20,26 μT • vertical part wasn`t measured (we didn`t have a vertical magnetic needle) – but in the middle Eurepa is important

  10. Other methods for measuring small magnetic fields • proton precission magnetometers • optically pumped magnetometers • overhauser magnetometers • fluxgate magnetometers

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