A) \[8\,m\]
B) \[800\,m\]
C) \[8\,km\]
D) \[80\,km\]
Correct Answer: C
Solution :
[c] \[\lambda =3m,\,\,H=100m,\,\,h=60m\] Path difference between direct wave and wave obtained ofter reflection from earth surface is \[\frac{2\pi }{\lambda }\left( \frac{2Hh}{d} \right)+\pi =2\pi \] or \[\left( \frac{4Hh}{\lambda d} \right)=1\] or \[d=\frac{4Hh}{\lambda d}\] \[\Rightarrow \,\,\,\,\,\,d=\frac{4\times 100\times 60}{3}=8\times {{10}^{3}}\] or \[8\,km\]
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