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 refers to the bending and spreading of waves as they encounter obstacles or openings, which allows them to propagate in different directions. When an AM radio wave meets a mountain or any other significant barrier, it does not simply stop. Instead, the wave diffracts around the edges of the obstacle, allowing the signal to continue traveling and reaching the receiver located on the other side of the mountain.

This characteristic is particularly relevant for lower frequency AM signals, as they have longer wavelengths that are more likely to bend around obstacles compared to higher frequency signals. This capability to propagate even when faced with barriers enables listeners in areas that might otherwise be out of range due to geographical obstacles to successfully receive AM broadcasts.

While refraction, reflection, and interference are also important phenomena in wave propagation, they do not specifically account for the way in which AM signals manage to navigate around large objects like mountains, making diffraction the most suitable explanation.