The four-current density $K^\nu$ embeds both the charge density ($\rho$) and the current density ($\mathbf{J}$) into a single four-vector.

What physical quantities are embedded in the four-vector (four-current density)-L.mp4

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1. How does the four-dimensional spacetime coordinate relate to the relativistic formulation of Maxwell's equations?
2. What physical quantities are embedded in the four-vector (four-current density)?
3. What physical quantities are embedded in the electromagnetic field tensor? </aside>