In this experiment we will measure the magnitude of the horizontal component of the Earth's Magnetic field by the use of an instrument called a tangent galvanometer.
A tangent galvanometer consists of a number of turns of copper wire wound on a hoop. At the center of the hoop a compass is mounted. When a direct current flows through the wires, a magnetic field is induced in the space surrounding the loops of wire. This magnetic flux is designated by Bi . The strength of the magnetic field induced by the current at the center of the loops of wire is given by Amperes law:
Induced Bi = [pic].
where μo is the permeability of free space and has the value of 4π x 10-7 N/A2, N is the number of turns of wire, I is the current through the wire, and R is the radius of the loop. When the wire loops of the tangent galvanometer are aligned with the magnetic field of the Earth, and a current is sent through the wire loops, then the compass needle will align with the vector sum of the field of the Earth and the induced field as shown in Figure 1.
The horizontal component of the magnetic field of the Earth is easily calculated from the following relation:
B of Earth = [pic].
SUPPLIES & EQUIPMENT:
Tangent galvanometer Ammeter Leads & connectors Reversing switch Ruler Rheostat, 20 Ω DC supply, 6 V Plywood board
1. Set up the apparatus on a board between tables as shown in Figure 2. Be sure to orient the loops exactly in the North-South direction. Orient the compass so that the needle is pointing to zero degrees.
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