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