Understanding Magnetic Forces Between Parallel Conductors

Forces Between Flows of Ampere Straight and Parallel: Definition

A conductor carrying an electric current creates a point around a magnetic field, which is directly proportional to the intensity of the current through the conductor I, and inversely proportional to the distance d from the conductor to the point under consideration.

If you place a conductor carrying a current in a magnetic field, the field exerts an interaction on it that depends upon the value of field strength B, the current I flowing through the conductor, and the length of the conductor l. The direction of F is perpendicular to the plane determined by the vectors B and l. The meaning of the interaction is fixed by the right-hand rule.

When two conductors carrying electric currents are placed next to each other, each creates a magnetic field that interacts with the other conductor. Thus, two straight and parallel conductors carrying currents I₁ and I₂, separated by a distance d, interact with each other. As per Ampere's experiences, the force exerted by one conductor over a length l of the other is:

The direction of F corresponds to the line connecting the conductors (radial direction). It suffices to recall that F is perpendicular to B and l. (Figure)

The action that one conductor exerts on the other would be the same but in the opposite direction (law of action and reaction). (Figure)

As is clear from the graphs, the magnetic forces between parallel conductors are attractive if the currents circulate in the same direction, and repulsive if they circulate in opposite directions.

• Ampere Definition:

The above expression is taken as a basis to define the ampere as the unit of current in the SI system. This is defined for the currents that circulate through both conductors at a value of 1 Amp, and the distance that separates them d = 1 meter. Under these conditions, substituting these values in the above equation allows us to define the unit Ampere:

"One ampere is the unit of intensity of current flowing through two parallel conductors separated by 1 m, where each experiences a force of 2.10^-7 N per meter of conductor length, being attractive if currents flow in the same direction and repulsive if they flow in opposite directions."