The Physics
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Magnetic Field on Earth

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Zitzewitz, Paul & Neff, Robert. Physics. New York: Glencoe/McGraw-Hill, 1995. "An airplane traveling at 950 km/h passes over a high region where the Earth's magnetic field is 4.5 × 10−5 T and is nearly vertical." 45 μT
"Earth's Magnetic Field: 5 × 10−5 T" 50 μT
Sears, F. W. & Zemansky, M. W. University Physics, 3rd ed. part 2. 1964. "At Cambridge, Massachusetts the magnitude of the earth's field is about 5.8 × 10−5 T and has an angle of dip that was 73 degrees." 58 μT
Worldbook Encyclopedia, vol. 13. 1995. "The Earth's magnetic field at the surface was about ½ gauss." 50 μT

Magnetic forces are produced by the motion of charged particles such as electrons, indicating the close relationship between electricity and magnetism. Polarized magnets have north seeking and south seeking poles. Like poles repel one another and unlike poles attract. A magnetic field is a detectable force that exists at every point in the region around the magnet or electric current. Magnetic fields are usually represented by flux lines. At any point the direction of the magnetic field is proportional to the space between the flux lines. Where flux lines are farther apart the magnetic field is weaker.

The magnetic poles of the Earth do not correspond with geographic poles of its axis. The poles' position is not constant and varies from year to year. The Earth's magnetic field changes continually in both magnitude and direction. The angle of declination is the measure of the direction of the horizontal component of the Earth's magnetic field vector relative to its north. The angle of inclination is the distance between the horizontal component and the tangent to the flux lines. The measure of the Earth's magnetic field is estimated at about 5.0 × 10−5 tesla [T = kg/Cs = 1 N/Am].

Danielle Caruso -- 1999