Earth inductor: Coil spun in Earth's field makes voltage.

Earth inductor: Coil spun in Earth's field makes voltage. The 'Earth Inductor' is a simple generator, illustrating the principle that a changing magnetic field cutting across a loop of wire induces an electric current. In this case, the magnetic field is that of the earth. A coil of wire is rotated in the earth's magnetic field, generating an emf. A simple magnetized needle on a stand finds north. Both the dip-needle and inductor apparatus are aligned with north. The dip-needle indicates the angle of the magnetic flux coming up through the earth. The inductor apparatus frame is tilted so that the coil-frame is perpendicular to the Earth's magnetic flux. (I.E.: The frame is rotated from the horizontal by an angle equal to the compliment of the dip-needle angle.) When the coil is rotated, maximum emf is generated at 'A' and min is at 'B' (in the side-view drawing). The apparatus has commutators so that either an AC sinusoidal signal or DC rectified signal can be amplified and visually represented by the projection galvonometer.