A) 4
B) 6
C) 8
D) 12
Correct Answer: C
Solution :
Key Idea: According to law of length\[n\propto \frac{1}{l}\]. The frequency of tuning fork is given by \[n=\frac{1}{2l}\sqrt{\frac{T}{m}}\] Where \[l\] is length of string \[T\] is tension and \[m\] is mass per unit length of string. Given, \[{{l}_{ & 1}}=50\,\,cm,\,\,{{l}_{2}}=\left( 1-\frac{2}{100} \right)\times 50=49\,\,cm\]. \[\frac{{{n}_{1}}}{{{n}_{2}}}=\frac{{{l}_{2}}}{{{l}_{1}}}=\frac{49}{50}\] \[\Rightarrow \] \[{{n}_{2}}=\frac{50}{49}\times 392=400\,Hz\] Also number of beats per second (beat frequency) \[={{n}_{2}}-{{n}_{1}}=\]difference of the frequencies of sound-sources. \[=400-392=8\]You need to login to perform this action.
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