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
Methods
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 NS with the wire of the coil.
Number turns coil (n) = ____;
length of wire on one side = ______ m
3.
Energize and record data.
I(Amp) 
2
Left 
2
Right 
Ave
2 
nI 
Tan 2 




























































Results
and Analysis
1. Plot the (nI)
column vs tan 2
(xaxis). Calculate
the slope.
2. Calculate B_{e}
using the equation for a toroid solenoid coil:
µ_{o} =
4Bx10^{7}
Teslameter/A (permeability
constant of a vacuum).
Then let
B_{e} = B_{coil}
/ 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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