Q: A source of frequency n gives 5 beats/s, when sounded with a source of frequency 200 s-1. The second harmonic (2 n) gives 10 beats/s, when sounded with a source of frequency 420 s-1. n is equal to
(a) 200 s-1
(b) 205 s-1
(c) 195 s-1
(d) 210 s-1
Ans:(b)
Sol: Here, n = 200 ± 5
and 2 n = 420 ± 10
This is possible only when
n = 200 + 5 = 205