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Mechanical Properties Of Fluids

Question
CBSEENPH11020235

Two sitar strings A and B playing the note ‘Ga’ are slightly out of tune and produce beats of frequency 6 Hz. The tension in the string A is slightly reduced and the beat frequency is found to reduce to 3 Hz. If the original frequency of A is 324 Hz, what is the frequency of B?

Solution
Frequency of string A, fA = 324 Hz
Frequency of string B = fB 
Beat’s frequency, n = 6 Hz 
Beat's Frequency is given as, 
straight n space equals space open vertical bar straight f subscript straight A space plus space straight f subscript straight B close vertical bar space

6 space equals space 324 space plus-or-minus space space straight f subscript straight B space

straight f subscript straight B space equals space 330 space Hz space or space 318 space Hz
Frequency decreases with a decrease in the tension in a string.
This is because the frequency is directly proportional to the square root of tension.
It is given as, 
v ∝ √

Hence, the beat frequency cannot be 330 Hz. 
∴                  fB = 318 Hz.