A) 4
B) 6
C) 8
D) 12
Correct Answer: C
Solution :
\[n\propto \frac{1}{l}\] Þ \[\frac{\Delta n}{n}=-\frac{\Delta l}{l}\] If length is decreased by 2% then frequency increases by 2% i.e., \[\frac{{{n}_{2}}-{{n}_{1}}}{{{n}_{1}}}=\frac{2}{100}\] Þ \[{{n}_{2}}-{{n}_{1}}=\frac{2}{100}\times {{n}_{1}}=\frac{2}{100}\times 392=7.8\approx 8.\]
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