Section-C: Comprehension Type
At your laboratory’s location, the earth’s magnetic field has magnitude 1.0 × 10-4 T and points north. A long, straight wire (wire A) runs in a north-south direction along the laboratory floor. You know that the wire carries current from south to north, but you do not know the magnitude of the current. To find out, you place two other long, straight wires on the floor parallel to wire A. Wire B is 5.0 cm to the east of wire A and wire C is 10.0 cm to the east of wire B. You connect sources of emf to wires B and C so that a constant current of 1.0 A flows from south to north in wire B, while an adjustable amount of current flows in wire C. Wires A and C are attached rigidly to the floor, while wire B is able to slide around.
You find by experiment that wire B will indeed start to slide one way or the other unless there is a 3.0-A current in wire C that flows from south to north. If this is case, wire B remains at rest.
How much current is flowing in wire A?