Q.Explain ground-wave (surface-wave) propagation of an electromagnetic wave. Why is this mode used mainly for low- and medium-frequency broadcasting, and why does it fail to carry a signal very far at higher frequencies?

Ground-wave (or surface-wave) propagation happens when a radio wave travels by gliding along the surface of the earth rather than through free space or via reflection. It occurs with large, ground-mounted antennas of the kind used for standard AM broadcast, because efficient radiation needs an antenna comparable in size to the wavelength (at least about $\lambda/4$), and at the long wavelengths of low-frequency signals such antennas must necessarily be tall structures built on or near the ground. As the wave travels, it induces currents in the earth beneath it, and this induction steadily drains ener …