The question is not well presented.
There is ______ shift in sound frequency for observers towards whom the source is approaching.
Answer:
The gap should be filled with an apparent upward
Explanation:
The Doppler effect (also referred to as the Doppler shift) is the difference in frequency of a wave when related to an observer who has a relative movement to the wave source
The Doppler effect can be observed to occur with all types of waves - most notably water waves, sound waves, and light waves
The Doppler effect describes sound as an effect which is produced from a moving source of wave.
According to the Doppler effect;
When the source of waves in which there is an apparent upward shift in frequency for observers towards whom the source is approaching.
