Machine-translated by Google. Questions are authored in English.
Top

Discussion

A closed organ pipe and an open organ pipe have the same length. The ratio of the frequencies in their third mode of vibrations is

  • A.3 : 1
  • B.2 : 3
  • C.5 : 6
  • D.4 : 5
  • E.3 : 5

Answer: C

The ratio is 5 : 6.

A closed pipe supports only odd harmonics, \(\frac{v}{4L}, \frac{3v}{4L}, \frac{5v}{4L}, \ldots\), so its third mode is \(\frac{5v}{4L}\). An open pipe supports all harmonics, \(\frac{v}{2L}, \frac{2v}{2L}, \frac{3v}{2L}, \ldots\), so its third mode is \(\frac{3v}{2L}\).

\[ \frac{5v/4L}{3v/2L} = \frac{5}{6} \]

The other ratios do not match these two frequencies. Taking the closed pipe's third harmonic \(3v/4L\) instead of its third mode would give 1 : 2, and 3 : 5 compares the third and fifth harmonics of one pipe.

No comment is present. Be the first to comment.
Loading…

Post your comment

Please log in or register to post a comment.