Two identical straight wires are stretched so as to produce 6 beats per second when vibrating simultaneously. On changing the tension slightly in one of them, the beat frequency remains unchanged. Denoting the higher and the lower initial tension in the strings as T1,T2 respectively, then it could be said that while making the above changes in tension :
T1 was decreased
∴ v1 > v2
or f1 > f2 and f1−f2 = 6 Hz.
Now, if T1 is increased, f1 will increase or f1−f2 will increase. Therefore, (D) option is wrong.
If T1 is decreased, f1 will decrease and it may be possible that now f2−f1 become 6 Hz. Therefore, (C) option is correct.