The Doppler effect is the change in frequency of a sound or light wave as perceived by an observer when the source of the wave is moving relative to the observer.
The u formula, also known as the velocity formula, is used to calculate the velocity of the source or observer in relation to the speed of the wave. On the other hand, the f´ formula, also known as the frequency formula, is used to calculate the change in frequency of the wave.
The u formula should be used when the velocity of either the source or observer is known and the change in frequency needs to be calculated.
The f´ formula should be used when the change in frequency is known and the velocity of either the source or observer needs to be calculated.
One example of the Doppler effect is the change in pitch of a siren as a police car passes by. In this case, the f´ formula can be used to calculate the change in frequency of the siren's sound. Another example is the redshift observed in light from distant galaxies, which is caused by the expansion of the universe. In this case, the u formula can be used to calculate the velocity of the galaxies.