First slide
Beats
Question

An organ pipe, open from both ends produces 5 beats per second when vibrated with a source of frequency 200 Hz. The second harmonic of the same pipes produces 10 beats per second with a source of frequency 420 Hz. The frequency of source is 

Moderate
Solution

Initially number of beats per second = 5
 Frequency of pipe = 200 ± 5 = 195 Hz or 205 Hz  ...(i) 
Frequency of second harmonics of the pipe = 2n and number of beats in this case = 10
 2n = 420 ± 10  410 Hz or 430 Hz 
 n = 205 Hz or 215 Hz                         ... (ii) 
From equation (i) and (ii) it is clear that n = 205 Hz

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