The poynting vector is the power per unit area, so to find the power we must integrate it over the area through which it travels. since it travels parallel to the inner current (oops, i just gave away half the answer to part we must integrate it over the washer-shaped area between the two cables, since that is the area through which the power flux passes. that is, that 2πrdr is the area of a little washer of radius r; the integral is in polar coordinates. if physics is right, then the total power transmitted in the fields (calculated from that integral) should exactly equal the amount of power being put into the cable by the battery. prove that physics is right. d) for reasons that cannot be explained here (google "oliver heaviside" and "telegrapher's equations for more info), the speed of em waves, and thus the speed at which the power travels, in a transmission line is v /wlc. plug in the formulas from above to find a simple formula for v in a coax. remember the "impedance matching" problem from exam 2? to deliver maximum power to the load, the impedance zo should match the load. for a coax cable just as for an lc circuit, ζ.- e) determine the ratio of outer to inner radius, b/a, for a coax so that its impedance matches a 75ω load resistor. the dielectric constant is 2.4, so ε 2.4eo, but it is not a magnetic material, so μ-10.