20.49. Set Up: For a long, straight wire If the currents are in the same direction, their fields add. If a pair of wires carry current in opposite directions, their fields are in opposite directions and cancel. Solve: (a) (b) The fields of two pairs cancel and the net field is due to the remaining two wires. Reflect: In a typical household appliance cord there are two closely spaced conductors carrying current in opposite directions and the currents in the cord produce very little net magnetic field. 20.50. Set Up: The net magnetic field at each point is the vector sum of the fields due to each wire. For each wire and the direction of is determined by the right-hand rule described in Section 20.7. Let the wire with 12.0 A be wire 1 and the wire with 10.0 A be wire 2. Solve: (a) Point Q : The direction of is out of the page. The direction of is out of the page. Since and are in the same direction, and is directed out of the page. Point P
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