Q: An tuning fork of frequency 480 Hz produces 10 beats per second when sounded with a vibrating sonometer string. What must have been the frequency of the string if a slight increases in tension produces fewer beats per second than before ?
(a) 480 Hz
(b) 490 Hz
(c) 460 Hz
(d) 470 Hz
Sol: Frequency of tuning fork, n1 = 480 Hz
No. of beats/sec, m = 10
Frequency of string n2 =(480 ± 10) Hz
A slight increase in tension increases n2
As Number of beats/sec decreases, therefore m must be negative.
n2 = 480-10
= 470 Hz