Wave Motion 2 Question 20

20. Two vibrating strings of the same material but of lengths L and 2L have radii 2r and r respectively. They are stretched under the same tension. Both the strings vibrate in their fundamental modes. The one of length L with frequency v1 and the other with frequency v2. The ratio v1/v2 is given by

(2000, 2M)

(a) 2

(b) 4

(c) 8

(d) 1

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Answer:

Correct Answer: 20. (d)

Solution:

  1. Fundamental frequency is given by

v=12lTμ

(with both the ends fixed)

Fundamental frequency

v1lμ (for same tension in both strings) 

where, μ= mass per unit length of wire

=ρA(ρ= density )=ρ(πr2) or μrv1rlv1v2=(r2r1)(l2l1)=(r2r)(2LL)=1



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