Now we are ready to address the question “What is \Delta\widetilde{\bf E}({\bf r}) due to \Delta\widetilde{\bf J}({\bf r})?” Without doing any math, we know quite a bit about \(\Delta\widetild...Now we are ready to address the question “What is \Delta\widetilde{\bf E}({\bf r}) due to \Delta\widetilde{\bf J}({\bf r})?” Without doing any math, we know quite a bit about \Delta\widetilde{\bf E}({\bf r}). If we are sufficiently far from the origin, and the loss due to the medium is negligible, then we expect the phase of \Delta\widetilde{\bf E}({\bf r}) to change approximately at rate \beta where \beta is the phase propagation constant 2\pi/\lambda.
