What is the Doppler effect? - Leaving Cert Physics - Question e - 2021

The Doppler effect refers to the apparent change in the frequency or wavelength of waves in relation to an observer moving relative to the wave source.

When the source of the waves approaches the observer, the waves are compressed, leading to an increase in frequency (or a decrease in wavelength), which is perceived as a higher pitch of sound. Conversely, when the source moves away from the observer, the waves are stretched, resulting in a decrease in frequency (or an increase in wavelength), perceived as a lower pitch.

This phenomenon is observable in various types of waves, including sound and light, and is commonly experienced with moving vehicles, such as the changing sound of a siren as an ambulance passes by.