The reception of an AM-band radio signal over mountains can be explained by which principle of wave propagation?

The reception of an AM-band radio signal over mountains is best explained by the principle of diffraction. Diffraction occurs when radio waves encounter obstacles like mountains and bend around them. This bending allows the radio waves to propagate into areas that would otherwise be in shadow due to the presence of the obstacles.

In the context of AM-band signals, which typically have longer wavelengths, diffraction is particularly effective because these longer wavelengths can easily adapt to the contours of the terrain. As a result, listeners on the other side of a mountain can still receive the AM signal even when a direct line of sight is obstructed by the elevation.

While refraction also involves the bending of waves, it primarily deals with changes in wave speed as they pass through different mediums, which is less relevant in this scenario. Reflection refers to the bouncing back of waves when they hit a surface, but that won't enable reception beyond the mountains. Interference is the phenomenon where two or more waves superimpose to form a resultant wave, but it does not specifically address how signals propagate around obstacles. Thus, diffraction is the principle that accurately describes how AM signals can successfully navigate mountainous terrain.