Wave Mechanics Question 732
Question: A tuning fork vibrating with a sonometer having 20 cm wire produces 5 beats per second. The beat frequency does not change if the length of the wire is changed to 21 cm. the frequency of the tuning fork (in Hertz) must be
[UPSEAT 2000; Pb. PET 2004]
Options:
A) 200
B) 210
C) 205
D) 215
Show Answer
Answer:
Correct Answer: C
Solution:
Let the frequency of tunning fork be N As the frequency of vibration string $ \propto \frac{1}{length\ ofstring} $ For sonometer wire of length 20 cm, frequency must be (N + 5) and that for the sonometer wire of length 21cm, the frequency must be (N ? 5) as in each case the tunning fork produces 5 beats/sec with sonometer wire Hence $ n _{1}l _{1}=n _{2}l _{2} $
Therefore $ (N+5)\times 20=(N-5)\times 21 $
Therefore $ N=205Hz. $
BETA
