The Doppler Effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the source of the wave.
The Doppler Effect can cause the perceived sound level to change due to the change in frequency of the sound wave as it moves towards or away from the observer.
The sound level at 40m from a source of 20dB would depend on the direction of the sound source and the speed of the observer. If the observer is moving towards the source, the sound level may increase due to the decrease in wavelength, and vice versa.
Yes, the Doppler Effect can affect all types of waves, including light, water, and seismic waves.
The Doppler Effect has many practical applications, such as in radar and sonar technology, medical imaging, and the study of distant galaxies in astronomy.