## Last Week's Question

The ratio of the electric field strength to the magnetic field strength for a wave propagating in RG58 coaxial cable (Z0 = 50 Ω, εr =2.3) is,

1. 50 Ω
2. 250 Ω
3. 377 Ω
4. > 10 MΩ

The correct answer is "b". The ratio of the electric field strength to the magnetic field strength for a wave propagating in a transmission line is equal to the intrinsic impedance of the dielectric. In this example, the dielectric has a relative permittivity equal to 2.3. Therefore, the intrinsic impedance is $\eta =\sqrt{\frac{\mu }{\epsilon }}=\sqrt{\frac{{\mu }_{0}}{{\epsilon }_{0}{\epsilon }_{r}}}\approx \frac{377\text{\hspace{0.17em}}\Omega }{\sqrt{2.3}}\approx 250\text{\hspace{0.17em}}\mathrm{\Omega .}$