ATPL EASA Radio Navigation Practice Exam

The Doppler effect is a phenomenon that occurs when there is relative motion between a wave source and an observer. Specifically, it describes how the frequency of electromagnetic waves, such as light or radio waves, changes due to this relative motion. When the source of the waves moves towards the observer, the observed frequency increases, leading to a higher pitch in sound or a shift towards the blue end of the spectrum in light. Conversely, if the source moves away from the observer, the frequency decreases, resulting in a lower pitch for sound or a shift towards the red end of the spectrum for light.

This concept is fundamental in various fields, including telecommunications and astronomy, where it helps in understanding the movement of stars and galaxies, as well as in radar and navigation systems. The other options relate to different concepts; for example, changes in signal amplitude pertain to signal strength rather than frequency, modulation involves altering a carrier wave's characteristics, and the standard measurement of acoustic waves does not encompass the broader effect on frequency caused by movement.