Small Field

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# Small Field - PowerPoint PPT Presentation

Small Field. TMF 2004 Gymnasium Elišky Krásnohorské. 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. Measuring magnetic induction.

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### Small Field

TMF 2004

Gymnasium Elišky Krásnohorské

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
Measuring magnetic induction
• direct force measuring is not ideal
• using secondary field
• constant field, measuring angle size
• constant angle, variable magnetic field
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
Equation
• Bx - magnetic induction
• n - count of turns
• r - radius of coils
• d - distance of coils
• I – leak curent
•  - absolute permeability
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)
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
Other methods for measuring small magnetic fields
• proton precission magnetometers
• optically pumped magnetometers
• overhauser magnetometers
• fluxgate magnetometers