Final answer:
Two parallel wires will attract each other if currents flow in the same direction and repel if currents flow in opposite directions. The relationship is not based on the lengths of the wires but on the direction of the currents and the distance between the wires.
Step-by-step explanation:
The relationship between the currents in two parallel wires depends on the direction of the currents. When two parallel wires carry currents in the same direction, they attract each other due to the creation of magnetic fields which interact. This can be understood using the right-hand rule, which helps determine the direction of these magnetic fields and forces. Conversely, when the currents flow in opposite directions, the wires repel each other due to the opposite orientation of the magnetic fields generated. The current in the wires is not dependent on their lengths; hence, options 3 and 4 are incorrect. Instead, the force per unit length between two long straight parallel currents is given by the Ampere's force law, which states that the force is directly proportional to the product of the currents and inversely proportional to the distance between them.
For example, two long straight wires that are parallel and a certain distance apart carrying currents in the same direction will experience magnetic forces that pull them together. If the currents are in opposite directions, they will push apart. The magnitude of this force can be calculated using formulas derived from Ampere's law.