**Experiment**

Experimental Setup

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

**Magnetic Moment**

Presented by

Hew Kai Ming

A0098123E

Magnetic field mapping on the surface of a spherical magnet using iron needles

Applications

Electromagnetic Induction

James Clerk

Maxwell

Maxwell's equations

Theory

(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

Vernier Calipers

- measure the diameter of loops

α = 90 degree

α = 0 degree

Comments

Conclusion

References

T vs I'

T vs I

T vs n

T vs d

2

T vs sin(α)

Definition of Magnetic Moment

Magnetic Torque

Newtonian Torque

Biot-Savart Law

=

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

Precision

- 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.

Accuracy

- 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.

Images

Electrical motor:

http://upload.wikimedia.org/wikipedia/commons/0/04/Electric_motor_cycle_2.png

Fan:

http://upload.wikimedia.org/wikipedia/commons/a/a3/The_Black_Beauty.jpg

Magnetic Moment:

http://upload.wikimedia.org/wikipedia/commons/1/19/Magnetic_moment.PNG

Biot-Savart law image:

http://scientificsentence.net/Electromagnetics/Physics/BiotSavart/Biot-Savart.jpg

Content

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

Zero Error