Question

34. When the tension on the sonometer wire is increased by 15 N. its frequency is doubled
The original tension is
(B)
5 N
(A) Zero
(D)
15 N
(C) 10 N​

Answer 1

When a mass of 20kg is suspended from the free end of the wire, the tenstion in the string=20g.

When tension in the string is as shown in the figure, we consider free body diagram of each block. Let the acceleration of the 14kg block be downwards.

Thus 14a=14g−T

And 6a=T−6g

⟹T=8.4g

Thus tension in the sonometer wire=2T=16.8g<20g

Thus the tension in this case is lesser.

Since frequency ∝

T

, the fundamental frequency becomes smaller.