A) 5
B) 7
C) 8
D) 3
Correct Answer: B
Solution :
Key Idea The number of beats will be the difference of frequencies of the two strings. |
Frequency of first string \[{{f}_{1}}=\frac{1}{2{{l}_{1}}}\sqrt{\frac{T}{m}}\] |
\[=\frac{1}{2\times 51.6\times {{10}^{-2}}}\sqrt{\frac{20}{{{10}^{-3}}}}\] |
\[=137.03\,Hz\] |
Similarly, frequency of second string |
\[=\frac{1}{2\times 49.1\times {{10}^{-2}}}\sqrt{\frac{20}{{{10}^{-3}}}}\] |
\[=144.01\] |
Number of beats\[={{f}_{2}}-{{f}_{1}}=144-137\] |
= 7 beats |
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