Another Beat Frequency Question

[Alain12345]

I have another beat frequency question. I understand how to get the possible frequencies of a string or tuning fork, but I don't know how to determine which one is the original frequency.

When a guitar string is sounded against a 440 Hz tuning fork, twelve beats are heard in two seconds.
a) What are the possible frequencies of the string?
b) If the person tightens the string, the beat frequency decreases. What then is the original frequency of the string, and why?

 

[cscott]

So, I assume you know $\#beats = |f_1 - f_2|$:

Since the beat frequency decreases [tex]f_1[/itex] and $f_2$ must approach each other. If this is the case, which one would you pick?[/tex]