Waves - Result Question 53
55. 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
(a) $246 Hz$
(b) $240 Hz$
(c) $260 Hz$
(d) $254 Hz$
[2013]
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Answer:
Correct Answer: 55. (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 $254 Hz$
