Question

A fork gives 5 beats with a 40cm length of sonometer wire. If the length of the wire is shortened by 1cm, the number of beats is still the same. The frequency of the fork is
A. 385 Hz
B. 320Hz
C. 395Hz
D. 400 Hz

Answer 1

Correct Answer - C
`n_2 gt n gt n_1`
`n_2 - n=5`
`(n-n_1=5)/(n_2-n_1=10)`
`n_2/n_1 = l_1/l_2 = 40/39`
`(n_2-n_1)/(n_1) = (40-39)/(39) = 1/39`
`10/n_1 = 1/39 " " therefore n_1= 390`
`therefore n=n_1+5`
=390+5=395