A train whistling at constant frequency is moving towards a station at a constant speed V. The train goes past a stationary observer on the station. The frequency n′ of the sound as heard by the observer is plotted as a function of time t (Fig) . Identify the expected curve

This is a multiple choice answer as classified in NCERT Exemplar

(c) Let frequency of the source is n_o

Let the speed of sound wave in the medium is v

As observer is stationary

Apparent frequency n_a= $\frac{v}{v-v_s}{n}_o$

$\frac{v}{v-v_s}{n}_o=n_a{n}_o$

When the train is going away from the observer

Apparent frequency n_a= $\frac{v}{v-v_s}{n}_o$ = $n_a<n_o$

<p><span data-teams="true">This is a multiple choice answer as classified in NCERT Exemplar</span></p><p> (c) Let frequency of the source is n_o</p><p>Let the speed of sound wave in the medium is v</p><p>As observer is stationary</p><div><div><picture><source srcset="https://images.shiksha.com/mediadata/images/articles/1745487578phptz80Lk_480x360.jpeg" media=" (max-width: 500px)"><img src="https://images.shiksha.com/mediadata/images/articles/1745487578phptz80Lk.jpeg" alt="" width="210" height="86"></picture></div></div><p>Apparent frequency n_a=<span contenteditable="false"> <math> <mfrac> <mrow> <mrow> <mi>v</mi> </mrow> </mrow> <mrow> <mrow> <mi>v</mi> <mo>-</mo> <msub> <mrow> <mrow> <mi>v</mi> </mrow> </mrow> <mrow> <mrow> <mi>s</mi> </mrow> </mrow> </msub> </mrow> </mrow> </mfrac> <msub> <mrow> <mrow> <mi>n</mi> </mrow> </mrow> <mrow> <mrow> <mi>o</mi> </mrow> </mrow> </msub> </math> </span></p><p><span contenteditable="false"> <math> <mfrac> <mrow> <mrow> <mi>v</mi> </mrow> </mrow> <mrow> <mrow> <mi>v</mi> <mo>-</mo> <msub> <mrow> <mrow> <mi>v</mi> </mrow> </mrow> <mrow> <mrow> <mi>s</mi> </mrow> </mrow> </msub> </mrow> </mrow> </mfrac> <msub> <mrow> <mrow> <mi>n</mi> </mrow> </mrow> <mrow> <mrow> <mi>o</mi> </mrow> </mrow> </msub> <mo>=</mo> <msub> <mrow> <mrow> <mi>n</mi> </mrow> </mrow> <mrow> <mrow> <mi>a</mi> </mrow> </mrow> </msub> <mo></mo> <msub> <mrow> <mrow> <mi>n</mi> </mrow> </mrow> <mrow> <mrow> <mi>o</mi> </mrow> </mrow> </msub> </math> </span></p><p>When the train is going away from the observer</p><p>Apparent frequency n_a=<span contenteditable="false"> <math> <mfrac> <mrow> <mrow> <mi>v</mi> </mrow> </mrow> <mrow> <mrow> <mi>v</mi> <mo>-</mo> <msub> <mrow> <mrow> <mi>v</mi> </mrow> </mrow> <mrow> <mrow> <mi>s</mi> </mrow> </mrow> </msub> </mrow> </mrow> </mfrac> <msub> <mrow> <mrow> <mi>n</mi> </mrow> </mrow> <mrow> <mrow> <mi>o</mi> </mrow> </mrow> </msub> </math> </span>=<span contenteditable="false"> <math> <msub> <mrow> <mrow> <mi>n</mi> </mrow> </mrow> <mrow> <mrow> <mi>a</mi> </mrow> </mrow> </msub> <mo>&lt;</mo> <msub> <mrow> <mrow> <mi>n</mi> </mrow> </mrow> <mrow> <mrow> <mi>o</mi> </mrow> </mrow> </msub> </math> </span></p>

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