Question

Kevin is standing outside a railway station. He can know whether a train is approaching the station or departing from the sound it makes. Which principle of sound waves is he using?

Answer 1

Kevin is using the principle of Doppler effect to recognize whether a train is approaching or departing from the sound it makes. The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. In this case, as the train approaches the station, the frequency of the sound waves it produces increases, resulting in a higher pitch. As the train moves away from the station, the frequency of the sound waves decreases, resulting in a lower pitch. By listening to the pitch of the sound, Kevin can tell whether the train is approaching or departing.