Two long fixed parallel wires, A and B, are 10 cm apart in air and carry 40 A and 20 A, respectively, in opposite directions. Determine the resultant field (a) on a line midway between the wires and parallel to them and (b) on a line 8.0 cm from wire A and 18 cm from wire B. (c) What is the force per meter on a third long wire, midway between A and B and in their plane, when it carries a current of 5.0 A in the same direction as the current in A?
The Attempt at a Solution
How do you determine the sign of a magnetic field? I can calculate a magnetic field. How do you calculate a resultant field? I guessed the signs and put them on the paper, but I have no clue why they belong there. The answers are within the uploads. I am only concerned about parts a and b.