Magnetic Field of Earth  (B e )
Obj:  Measure the horizontal (H) component of the Earth's Magnetic Field

Introduction:  A magnetic compass needle will align itself with the horizontal component of the earth's magnetic field.  If there are other magnetic fields around the compass, its alignment will represent the resultant of the several fields.  This experiment will use the known field of a square coil and the resultant field to determine the earth's unknown magnetic field.  

              coil field  +  earth field  =  resultant field
Materials:  compass, DC power, 1S 10W power resistor, coil setup, ammeter
1.  Place the compass in the exact center on the aluminum table within the coil using the polar graph paper.
2.  Align the compass exactly N-S with the wire of the coil. 

            Number turns coil (n) = ____;  length of wire on one side = ______ m

3.  Energize and record data.


2 Left

2 Right

Ave 2


 Tan 2





























































Results and Analysis
1.  Plot the (nI) column vs tan
2 (x-axis).  Calculate the slope.
2.  Calculate Be  using the equation for a toroid solenoid coil:
            o  =  4
Bx10-7 Tesla-meter/A  (permeability constant of a vacuum).   Then let    Be  =  Bcoil / tan 2   
3.  Calculate % error using Geological Survey data such as Geomag.
4.  What effect does the structural steel in the high school have on the magnetic field? Explain the concept of permeability in magnetic fields.

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