Question

How will you align the compass and the large coil in earths magnetic field to get meaningful data? What measurements and calculations will you make?

Answer 1

To first approximation the magnetic field of the earth is a dipole field. This means that near the magnetic polesthe fields is perpendicular to the ground , whereas half way between the poles it is parallel to the ground. Note that we've avoided the use of words like north pole"and equator" , as the magnetuc poles do notcoincide with the geographic poles. In fact the magnetic poles are tilted away from the Earths axis of rotation by about 11 degrees . Today we wil use some very simple tools to measure the magnetic field of the earth.

                    Our first tool is compass. it will point towards "local north" what this means is that it will align itself with the magnetic field at its position.

                     We will use loops of wire to create an external magnetic field. consider the law of BIOT and SAVARTS

dB = ( mu₀ i dl Xr) /( 4 * pi r^2)

where r is the cross product is a unit vector

Imaginea segment pf wire running from -a to +a . At the halfway point we want to know what the field is a distance X away from the wire . If we integrate the previous equations , we will get

B = (mu₀ i G) / ( 4 * pi )

where G is a geometrical factor

G = 2a / ( x( x^2 +a^2)^1/2)