Question | Answer |
What happens when the sound source is approaching the observer? | The wavelength between the sound waves closest to the observer become smaller |
What happens to the frequency? Use the formula c=fλ | From this, we see that the frequency is inversely proportional to the wavelength: f=\[\frac{c}{λ}\] |
So, when the wavelength becomes smaller, the frequency becomes bigger | Thus, the noise from the sound source appears louder |
We can use this theory and a formula to calculate the apparent frequency of the source | It's important to note that the frequency itself doesn't change, it's an apparent change |
We use the formula f'=\(\frac{v}{v±vs}\)f | f' = Apparent frequency v= Speed of wave vs = Velocity of the source f = frequency of the source |
When the source is moving away, we use a minus on the bottom of the fraction: | f'=\(\frac{v}{v-vs}\)f |
Just remember that the apparent frequency is going to be greater, | So the bigger the smaller fraction is, the bigger f' will be, so use the minus! |
And check your answers, if you know the object is approaching but you get a smaller apparent frequency... | You've gone wrong somewhere!!! |
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