The sources are the charge density ($\rho$) and current density ($\mathbf{J}$), which are embedded in the four-vector $K^\nu$ (four-current density).

What are the sources for the inhomogeneous Maxwell's equations-L.mp4

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1. What are the sources for the inhomogeneous Maxwell's equations?
2. Why are Gauss's Law and the Ampère-Maxwell Law collectively called the inhomogeneous Maxwell's equations? </aside>