Question

(a) Consider two parallel wires running 2 cm apart. Each wire carries a current of 10 A running in the same direction (such a current is of the order of a large household current to power electrical devices). Sketch the set-up and calculate the magnitude of the force per unit length between the wires. Indicate the direction of the forces acting on the wires in your sketch.

(b) If you are surprised by the round number consider that this experimental set-up was used to originally define a current of 1 A in magnitude, i.e a current of 1 A corresponds to the current that runs through two parallel wires that experience a force per meter of length of 2 × 10−7 N / m. Why do you think physicists defined the unit of Ampere this way rather than by counting charges moving through a wire?

Answer 1