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14.Waves and Sound
normal
A small source of sound moves on a circle as shown in the figure and an observer is standing on $O.$ Let $n_1,\, n_2$ and $n_3$ be the frequencies heard when the source is at $A, B$ and $C$ respectively. Then
A
$n_1\,\, >\,\, n_2\,\, >\,\, n_3$
B
$n_2\,\, >\,\, n_3\,\, >\,\, n_1$
C
$n_1\,\, =\,\, n_2\,\, >\,\, n_3$
D
$n_2\,\, >\,\, n_1\,\, >\,\, n_3$
Solution
At point $A$, source is moving away from observer so apparent frequency $n_1\, < \,n$ (acutal frequency). At point $B$ source is coming towards observer so apparent frequency $n_2\, >\, n$ and point $C$ source is moving perpendicular to observer so $n_3\,\, =\,\, n$ . Hence $n_2\, >\, n_3\, >\, n_1$ .
Standard 11
Physics
