A) \[f,\,\,1,\,\,2\,\lambda \]
B) \[0.8f,\,\,0.8\lambda \]
C) \[1.2\,f,\,\,1.2\,\lambda \]
D) \[1.2\,f,\,\lambda \]
Correct Answer: D
Solution :
| When an observer moves towards an stationary source of round, then apparent frequency heard by the observer increases. The apparent frequency heard in this situation |
| \[f'=\left( \frac{v+{{v}_{0}}}{v-{{v}_{s}}} \right)\,f\] |
| As source is stationary hence, \[{{v}_{s}}=0\] |
| \[\therefore \] \[f'=\left( \frac{v+{{v}_{0}}}{v} \right)\,f\] |
| Given, \[{{v}_{0}}=\frac{v}{5}\] |
| Substituting in the relation for \[f',\] we have |
| \[f'=\left( \frac{v+v/5}{v} \right)f\] |
| \[=\frac{6}{5}f=1.2\,f\] |
| Motion of observer does not affect the wavelength reaching the observer, hence, wavelength remains \[\lambda \]. |
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