posted by Lanise .
Two long, parallel wires separated by 50 cm each carry currents of 3.0 A in a horizontal direction.
Find the magnetic field midway between the wires if the currents are in the same direction.
Find if they are in opposite directions.
Have you heard of Ampere's law? That is what you need to use.
The answer should be obvious for the same-direction case. For the opposite-direction case, double the field due to a single wire.