Waves - Result Question 42

44. The fundamental frequency of a closed organ pipe of length $20 cm$ is equal to the second overtone of an organ pipe open at both the ends. The length of organ pipe open at both the ends is

[2015]

(a) $100 cm$

(b) $120 cm$

(c) $140 cm$

(d) $80 cm$

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Answer:

Correct Answer: 44. (b)

Solution:

  1. (b) Fundamental frequency of closed organ pipe,

$v_c=\frac{v}{41_c}$

Fundamental frequency of open organ pipe

$v_0=\frac{v}{2 1_0}$

Second overtone frequency of open organ pipe $=\frac{3 v}{2 l_0}$

From question, $\frac{v}{4 l_c}=\frac{3 v}{2 l_0}$

$\Rightarrow 1_0=61_c=6 \times 20=120 cm$



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