Linear Superposition of waves ?

Question

Two tuning forks vibrate at frequencies f1 and f2 respectively (f1 ≠ f2) and produce sound waves of equal amplitude. Describe how the sound intensity heard by an observer varies and explain, with reference to the principle of linear superposition, why this variation in sound intensity occurs.

 

This is worth 9 marks !!! No idea where to even start. 

 

b) A third tuning fork of known frequency f3 (f3 > f1, f2) is also available. Describe how you could use this tuning fork to determine which of the frequencies f1 or f2 is the largest. 

 

This is 5 marks.  Thought these were a bit much asking at this level.

 

 

Answer 1

Take a look at the following image. For part a.

 

https://www.wyzant.com/resources/files/507935/linear_superposition_of_waves

 

Each tuning fork will produce a pure (almost pure sine wave). As you can see from the image the new sound will increase and decrease as the 2 sine waves comes into and out of phase with each other.

 

For part B the tuning fork that is closest to the frequency f3 will produces the smallest variation in sound in the resultant beat frequency. That is the closer 2 sine waves are together in frequency the less dramatic is the beat frequency. Since f3 frequency is greater than f1 and f2, the one that produces the smallest variation in sound in the beat frequency will be the highest frequency tuning fork.