A) 9:8
B) 8:9
C) 1:1
D) 9:10
Correct Answer: A
Solution :
\[f={{f}_{o}}\left( \frac{v+{{v}_{o}}}{v-{{v}_{s}}} \right)\] Apparent frequency when the source is approaching the observer\[={{f}_{1}}\] \[\therefore \]\[{{f}_{1}}={{f}_{0}}\left[ \frac{v+o}{v-20} \right]\] Apparent frequency when the source recedes from the observer\[={{f}_{2}}\] \[\therefore \]\[{{f}_{2}}={{f}_{o}}\left[ \frac{v}{v-(-20)} \right]={{f}_{o}}\left[ \frac{v}{v+20} \right].\] \[\therefore \] \[\frac{{{f}_{1}}}{{{f}_{2}}}=\frac{v+20}{v-20}=\frac{340+20}{340-20}=\frac{9}{8}\] Hence, the correction option is [a].
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