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An investigation on linearity relation of magnetic torque as
Transcript of An investigation on linearity relation of magnetic torque as
An investigation on linearity relation of magnetic torque as a function of magnetic field strength, magnetic moment and angle between magnetic field and magnetic moment in a uniform magnetic field
Hew Kai Ming
Magnetic field mapping on the surface of a spherical magnet using iron needles
(1) Torsion Dynamometer; (2) Helmholtz Coil; (3) Conductor loop; (4) Multimeter (Helmholtz Coil's Current); (5) Constanter (power source for Helmholtz Coil);
(6) Multimeter （Conductor loop's current);
(7) Power supply (power source for conductor loop)
Conductor loops with different diameters and number of turns
- measure the diameter of loops
α = 90 degree
α = 0 degree
T vs I'
T vs I
T vs n
T vs d
T vs sin(α)
Definition of Magnetic Moment
Sources of Uncertainties
- Some of the holders of the conductor loops (especially the 3-turns one) have melted as a result of subjected to high temperature due to the dissipated heat as current passes through the conductor.
- It is suspected those insulated impurities somehow are incorporated into the conductor, and slightly changing its property, i.e. conductivity.
Uneven diameter of Conductor loops
- A fluctuation up to 4mm is realized for the data collected.
- Minimized by making 3 measurements for each conductor used and then calculating the average diameter.
- In T vs n case, however, the areas are assumed to be the same and this may not be true.
Precision & Accuracy
- From the
- From the product description " 3.5mT at 5A", the theoretical value of the constant c is 0.000700 .
- The experimental value is 0.000709 .
- The percentage discrepancy of average c is 1.36%. Max % discrepancy is 4.37% (T vs n), while min. is 0.75% (T vs sin(α)).
- The result can be considered precise.
- The percentage uncertainty of the average c is 1.15%.
- The max. % uncertainty is 7.42% (T vs n), while the min. one is 0.67% (T vs I').
- Besides the two currents cases, all have exceeded 5%.
- The results are not very accurate.
Biot-Savart law image:
1) Magnetic moment laboratory manual
2) PHYWE Operating instruction: Torsion dynamometer 0.01 N
3) PHYWE Operating instruction: Helmholtz’s Coil
4) David J. Griffith. "Introduction to Electrodynamics" (3rd Edition), published by Prentice Hall, 1999. pg215, pg255-260.
Property of the conductor loops