A) \[\left( \frac{21}{19} \right)n\]
B) \[\left( \frac{20}{21} \right)n\]
C) \[\left( \frac{21}{20} \right)n\]
D) \[\left( \frac{19}{20} \right)n\]
Correct Answer: A
Solution :
From Dopplers effect, the perceived frequency (n) is given by \[n=\left( \frac{v+{{v}_{o}}}{v-{{v}_{s}}} \right)n\] where v is velocity of sound, \[{{v}_{o}}\] of observer and \[{{v}_{s}}\] of source. Given, \[{{v}_{o}}=\frac{v}{20},\,\,\,{{v}_{s}}=\frac{v}{20}\] \[\therefore \] \[n=\left( \frac{v+\frac{v}{20}}{v-\frac{v}{20}} \right)n\] \[\Rightarrow \] \[n=n\left( \frac{21\,v}{19\,v} \right)=\left( \frac{21}{19} \right)n\]
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