On the electromotive force in moving conductors

Abstract

This article attempts to clarify the role of the magnetic force and the ‘‘rotational’’ component of the electric field in calculating the induced electromotive force in a circuit having a moving part. For this purpose, an example where both terms occur is analyzed.

On the role of induced fields in railguns

“…Namias [3] treats this in terms of motional emf , i.e., the motion of a conductor through a magnetic field. Delellis et al [5], on the other hand argue that the emf is generated by a combination of flux creation and motional emf. As a third example, Zahn [6] addresses this purely in terms of flux creation.…”

“…Carpenter [7] also assumes that the emf from armature motion is motional. Delellis et al [8] on the other hand, conclude that the emf associated with moving armatures in a railgun arises from a mixture of motional and flux creation contributions. As another example, Zahn [9] treats the emf generated by armature motion as flux creation (as we do here); he only computes the net emf and does not distinguish between uniform flux creation and local flux creation, however.…”

“…In the spirit of the Biot and Savart law, this new segment generates sufficient flux Bvh at that location to constantly fill the area behind the armature defined by x as the armature moves. Now, compute the left hand side of equation (8). Ignore the underlying physics and obtain d /dt from the geometry: with constant I , B is constant, and the area increases at the rate vh, giving d /dt = Bvh, which, in effect, sets the upper limit on the sum.…”