A source of sound emits sound waves at frequency $f_0$. It is moving towards an observer with fixed speed $v_s$ ($v_s < v$, where $v$ is the speed of sound in air). If the observer were to move towards the source with speed $v_0$, one of the following two graphs ($A$ and $B$) will given the correct variation of the frequency $f$ heard by the observer as $v_0$ is changed The variation of $f$ with $v_0$ is given correctly by
  • Agraph $A$ with slope $ = \,\frac{{{f_0}}}{{\left( {v + {v_s}} \right)}}$
  • Bgraph $B$ with slope $ = \,\frac{{{f_0}}}{{\left( {v - {v_s}} \right)}}$
  • Cgraph $A$ with slope $ = \,\frac{{{f_0}}}{{\left( {v - {v_s}} \right)}}$
  • Dgraph $B$ with slope $ = \,\frac{{{f_0}}}{{\left( {v + {v_s}} \right)}}$
JEE MAIN 2015, Diffcult
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