(Finding the Magnetic Field Strength)
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Contents
Diagram 1.1
Data Table 1.1


The purpose of this preliminary investigation was to determine the specific magnetic fields of the magnets I was using in my observation. After going through many different setups. I decided that the best way would be to create a uniform magnetic field that canceled the magnet's field lines. I would then use a small, very sensitive test magnet to find the current needed to cancel the unknown magnet's field (This would be found at the point where the compass magnet could go either direction perpendicular to the field). I made the solenoid out of a pop bottle by neatly wrapping an insulated wire around it. The solenoid had 198 turns in a distance of 0.123952 meters.
Diagram 1.1
TOC
(Solenoid Set-Up)

The equation for a magnetic field created in the center of a solenoid is:
B =
l o*(N/L)*I, where N/L is the number of loops per length.
For me this value was
198/0.123952, or 1597.4, so, simplified my equation is

B 0.00200734*I

Since I had no choice but to do this on Earth, I had to deal with the magnetic field already in existence. To solve this I always had the magnetic field lines facing from north to south. I found the Earth's magnetic field to be at a current of 10.33mA, which corresponds to a magnetic field of 2.07358E-5 Teslas. This is actually fairly close to the 5.00E-5 Teslas give by Giancoli (Giancoli, 1991: 533). I don't think that this difference of about 2.9264E-5 Teslas represents an error, but an angle of dip of the Earth's B-field. In other words the horizontal component is 2.07358E-5 Teslas. This is supported by the fact that in Cambridge, Massachusetts the horizontal component is about 1.7E-5 teslas, which isn't far magnetically, from Portland, Oregon (Zemansky, 699). Therefore, for my experiment the equation for the actual magnetic field of the magnet would be:
Bmagnet + Bearth = Bsolenoid

Data Table 1.1
TOC

Magnetic Field Data

(Small Ceramic Magnet)

Meters

mA

Solenoid
B-Field

Magnet
B-Field

0.06033

246.2

0.00049

0.00047

0.0635

211.4

0.00042

0.0004

0.06985

171.5

0.00034

0.00032

0.0762

126.8

0.00025

0.00023

0.0889

86.8

0.00017

0.00015

0.1016

63

0.00013

0.00011

0.1143

46.2

9.3E-05

7.2E-05

0.127

37.2

7.5E-05

5.4E-05

0.1397

30.65

6.2E-05

4.1E-05

0.1524

26.2

5.3E-05

3.2E-05

0.1651

22.34

4.5E-05

2.4E-05

0.1778

20.65

4.1E-05

2.1E-05

0.1905

18.91

3.8E-05

1.7E-05

0.2032

16.6

3.3E-05

1.3E-05

0.2159

15.9

3.2E-05

1.1E-05

0.2286

15.51

3.1E-05

1E-05

0.2413

14.87

3E-05

9.1E-06

0.254

14.42

2.9E-05

8.2E-06

data file

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