Question

An "E" tuning fork with a frequency of 329 Hz is used to test the "E" note of a piano. Four beats are heard. This means _____.

The piano key is in tune.
The piano key is out of tune and has a frequency of 333 Hz.
The piano key is out of tune and has a frequency of 325 Hz.
The piano key is out of tune and has a frequency of either 325 or 333 Hz

Answer 1

The piano key is out of tune and has a frequency of either 325 or 333 Hz

Answer 2

The correct choice is

The piano key is out of tune and has a frequency of either 325 or 333 Hz

Beat frequency has been given as 4 Hz. hence the frequency must be above or below the given frequency of 329 Hz by 4 Hz. To get the upper level of frequency we add the beat frequency to the given frequency. To get the lower level, we subtract the beat frequency from the given frequency

f' = 329 + 4 = 333 Hz

and

f'' = 329 - 4 = 325 Hz