- #1
cianfa72
- 2,352
- 253
- TL;DR Summary
- About the role of electromotive force in Maxwell equations formulation
Hi,
reading Griffiths - Introduction to Electrodynamics I'm confused about his claims in section 7.1
My point is that the job of electromotive force ##f## is actually produce the "movement/drift" of free charges against the electromagnetic field, so ##f## should not be given by the Lorentz force as in Eq. 7.1.
In other words the fields ##\vec E## and ##\vec B## entering in the formula above seem to be the "external cause" of current flux/current density ##\vec J## (through the Lorentz force acting on the free charges) when they are not.
reading Griffiths - Introduction to Electrodynamics I'm confused about his claims in section 7.1
In principle, the force that drives the charges to produce the current could be anything - chemical, gravitational, or trained ants with tiny harnesses. For our purposes, though, it’s usually an electromagnetic force that does the job. In this case Eq. 7.1 becomes $$\vec J = \sigma(\vec E + \vec v \times \vec B)$$
My point is that the job of electromotive force ##f## is actually produce the "movement/drift" of free charges against the electromagnetic field, so ##f## should not be given by the Lorentz force as in Eq. 7.1.
In other words the fields ##\vec E## and ##\vec B## entering in the formula above seem to be the "external cause" of current flux/current density ##\vec J## (through the Lorentz force acting on the free charges) when they are not.
Last edited: