The Doppler Effect - Observer is moving as well

Question	Answer
The formula f'=\(\frac{v}{v±vs}\)f does not hold if the observer is moving too	We now use the equation f'=\(\frac{v±vo}{v±vs}\)f
Where vo represents the velocity of the observer	But when do we use +vo, and when do we use -vo?
If the observer is moving away from the source, we use -vo	The relative frequency will decrease, and the smaller the top of the fraction is, the smaller the relative frequency is
If the observer is moving towards from the source, we use +vo	The relative frequency will increase, and the bigger the top of the fraction is, the bigger the relative frequency is
Don't get vs and vo mixed up. Vs is the velocity of the source of the sound	And vo is the velocity of the observer
You will only use this equation for more difficult examples	Make sure that everything in the equation has the same units
For example, if the source is moving at 20 km/h, and the observer is moving at 10 m/s...	Change them both into m/s or km/h. If you don't you will get the wrong answer
And always check if the frequency is in Hz or kHz.	Minor details like this can make a big difference in an exam

Resource summary

	Created by leonie.examtime over 10 years ago

	Copied by ed.wilson89 over 10 years ago