Enter the actual speed of the source, the source frequency, the observer speed, and the speed of sound in the medium into the calculator to determine the observed frequency due to the Doppler effect.
Observed Frequency Formula
The following formula is used to calculate the observed frequency:
f' = f * ((v + vo) / (v - vs))
Variables:
- f’ is the observed frequency (Hz)
- f is the source frequency (Hz)
- v is the speed of sound in the medium (m/s)
- vo is the observer speed (m/s)
- vs is the actual speed of the source (m/s)
To calculate the observed frequency, multiply the source frequency by the ratio of the sum of the speed of sound and the observer speed to the difference between the speed of sound and the actual speed of the source.
What is Observed Frequency?
Observed frequency is the frequency of a wave, such as sound or light, as detected by an observer. It is affected by the relative motion between the source of the wave and the observer, a phenomenon known as the Doppler effect. When the source and the observer are moving closer together, the observed frequency increases; when they are moving apart, the observed frequency decreases.
How to Calculate Observed Frequency?
The following steps outline how to calculate the Observed Frequency:
- First, determine the source frequency (f) in Hertz (Hz).
- Next, determine the actual speed of the source (vs) in meters per second (m/s).
- Next, determine the observer speed (vo) in meters per second (m/s).
- Next, determine the speed of sound in the medium (v) in meters per second (m/s).
- Next, gather the formula from above = f’ = f * ((v + vo) / (v – vs)).
- Finally, calculate the Observed Frequency (f’) in Hertz (Hz).
- After inserting the variables and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
source frequency (f) = 440 Hz
actual speed of the source (vs) = 10 m/s
observer speed (vo) = 5 m/s
speed of sound in the medium (v) = 343 m/s
