Magnetometer
lastmod 2018-08-17created 2014-05-032 edits
An instrument for measuring magnetic fields and magnetic moments. It consists of a small magnetic needle, a thin wire whose torque is negligible, and a reading device. For example, to measure the magnetic moment of a bar magnet, place the magnet in the east-west direction and measure the magnetic field Hx produced at the small needle of the magnetometer at a distance D from it. If the length of the magnet is l, the pole strength is m, the magnetic moment is M=ml, and D≫l, then Hx≒2M/D3. Since the small needle of the magnetometer points in the resultant direction θ of Hx and the horizontal component H of the Earth's magnetic field, the relation Hx=Htanθ holds. Therefore, the magnetic moment of the magnet is obtained from M= 1/2D3 Htanθ.
For reference, this page can also be reached via Geo-magnetic sensor.