Engineering Homework Help

We know the surface of the earth is a good reflector at AM radio frequencies (50 to 200 kHz), yet a poor reflector in the visible (1014 Hz). At what RF frequency will the electrical properties of the earth transition from conductive to dielectric? Explain your result. (Use σ = 5×103 S/m, µ r = 1, and ε r = 8 for the earth.) (Hint: consider reflection from the ground and/or attenuation into the ground.)