A) Frequency different, amplitude same
B) Frequency same, amplitude same
C) Frequency same, amplitude different
D) None of the above
Correct Answer: A
Solution :
Key Idea Number of beats is equal to difference in frequency. When two sound waves of slightly different frequencies, travelling in a medium along the same direction, superimpose on each other, the intensity of the resultant sound at a particular position rises and falls alternately with time. This phenomenon of alternate variation in the intensity of sound with time at a particular position, when two sound waves of nearly equal frequencies and same amplitude superimpose on each other is called beats. For the formation of distinct beats, frequencies of two sources of sound should be nearly equal ie, difference in frequencies of two sources must be small, say less than 10. In order to hear distinct beats, time interval between two successive beats must be greater than 1/10. Therefore, frequency of beats must be less than 10, ie, number of beats/second, which is equal to difference in frequencies of two sources must be less than 10. Hence, the two sources should be of nearly equal (but not same) frequencies.
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