Waves - Result Question 64
66. A source of sound gives 5 beats per second, when sounded with another source of frequency $100 / sec$. The second harmonic of the source, together with a source of frequency $205 / sec$ gives 5 beats per second. What is the frequency of the source?
(a) $95 sec^{-1}$
(b) $100 sec^{-1}$
(c) $105 sec^{-1}$
(d) $205 sec^{-1}$
[1995]
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Answer:
Correct Answer: 66. (c)
Solution:
- (c) Frequency of first source with 5 beats/ sec $=100 Hz$ and frequency of second source with 5 beats $/ sec=205 Hz$. The frequency of the first source $=100 \pm 5=105$ or $95 Hz$. Therefore, frequency of second harmonic of source $=210$ $Hz$ or $190 Hz$. As the second harmonic gives 5 beats/ second with the sound of frequency 205 $Hz$, therefore, frequency of second harmonic source should be $210 Hz$ or frequency of source $=105 Hz$.
