A) Increase by 0.5 %
B) Decrease by 5 %
C) Increase by 20 %
D) Increase by 50 %
Correct Answer: C
Solution :
Let initial speed of sound be v Therefore, frequency \[=\frac{v}{\lambda }\] (where, \[\lambda =\] wavelength) \[{{n}_{1}}=\frac{v}{\lambda }\] ?. (i) According to the question,\[{{n}_{2}}=\frac{\frac{6v}{5}}{\lambda }\] (When, increase the velocity \[=v+\frac{v}{5}=\frac{6v}{5}\]) \[{{n}_{2}}=\frac{6v}{5\lambda }\] ? (ii) The percentage (increase) \[=\frac{{{n}_{2}}-{{n}_{1}}}{{{n}_{1}}}\times 100\] \[=\frac{\frac{6}{5}\times \frac{v}{\lambda }-\frac{v}{\lambda }}{\frac{v}{\lambda }}\times 100=\frac{\left( \frac{6}{5}-1 \right)\frac{v}{\lambda }}{\frac{v}{\lambda }}\times 100\] \[=\frac{1}{5}\times 100=20%\] by increase
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