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BITSAT 2011 Paper

Section: Physics

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Question : 20 of 150

Marks: +1, -0

The fundamental frequency of an open organ pipe is 300 Hz. The first overtone of this pipe has same frequency as first overtone of a closed organ pipe. If speed of sound is 330 m/s, then the length of closed organ pipe is

41 cm
37 cm
31 cm
80 cm

Solution:

For open pipe, n =

\frac{v}{2l}

, when

n_0

is the fundamental frequency of open pipe.

∴ l =

\frac{v}{2n}

=

\frac{330}{2 \times 300}

=

\frac{11}{20}

As freq. of 1st overtone of open pipe = freq. of 1st overtone of closed pipe

∴ 2

\frac{v}{2l}

= 3

\frac{v}{4l'}

⇒ l' =

\frac{3l}{4}

=

\frac{3}{4} \times \frac{11}{20}

= 41.25 cm

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