Question

Problem 1: Birds on tree One bird can sing with the sound intensity level of 5 dB measured by the listener near the tree. Suppose there are many birds on the tree which all sing in phase with the same amplitude and frequency. The same listener measures the sound intensity level 25 dB at the same position as before. How many birds arc there on the trec? (i) 10 (ii) 25 iv) 50 v) 100

Answer 1

Let intensity of single bird at listened be I_1 w/m^2 or, 10 log I-1/I_0 = 5 dB 1 If there are in birds on the free then intensity of sound due to n birds is n^2I_1 Therefore 10 log n^2 I_1/I_0 = 25 dB 10 log n^2 + 10 log I_1/I_0 = 25 dB 10 log_10 n^2 + 5 dB = 25 dB 10 log I_1/I_0 = 5 using 1 2 log n = 2 n = 10 Answer b n = 10