Waves Ques 51
51. A source of unknown frequency gives $4$ beats/s, when sounded with a source of known frequency $250$ $ Hz$. The second harmonic of the source of unknown frequency gives five beats per second, when sounded with a source of frequency $513$ $ Hz$. The unknown frequency is
[2013]
(a) $246 $ $Hz$
(b) $240 $ $Hz$
(c) $260 $ $Hz$
(d) $254 $ $Hz$
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Answer:
Correct Answer: 51.(d)
Solution:
- (d) When sounded with a source of known frequency fundamental frequency
$=250 \pm 4$ $ Hz=254 $ $Hz$ or $246$ $ Hz$
$2^{\text{nd }}$ harmonic if unknown frequency (suppose) $254 $ $Hz=2 \times 254=508$ $ Hz$
As it gives $5$ beats
$\therefore 508+5=513$ $ Hz$
Hence, unknown frequency is $254 $ $Hz$
BETA
