Q: Ten tuning forks are arranged in increasing order of frequency in such a way that any two nearest forks produce 4 beats/s. The highest frequency is twice that of the lowest. Possible lowest and highest frequencies are

(a) 40 and 80

(b) 50 and 100

(c) 22 and 44

(d) 36 and 72

Ans: (d)

Sol: Let frequencies are :

x , x + 4 , x + 8 ………2x

The n^{th} term of A.P is

T_{n} = a + (n-1)d

2 x = x + (10 -1)×4

x = 36 Hz

Highest frequency = 2 x = 72 Hz