The amplitude of a standing sound wave in a long pipe closed at the left end is

Question

The amplitude of a standing sound wave in a long pipe closed at the left end is sketched in the diagram. The vertical axis is the maximum displacement of the air, and the horizontal axis is along the length of the pipe. What is the harmonic number for the mode of oscillation illustrated? You have only 2 tries!

Correct, computer gets: 5

14. [1pt]
The length of the pipe is 0.360 m. What is the pitch (frequency) of the sound? Use 341.0 m/s for the speed of sound in air.

Yes, Computer gets: 1.18E+03 Hz

15. [1pt]
The pipe is now held vertically, and a small amount of water is poured inside the pipe. The first harmonic frequency is then measured to be 293.6 Hz. Measuring from the bottom of the pipe, what is the level of the water?

I only need help with 15 but the above questions are required to answer it.  

Explanation / Answer

c) Let level of water H, If reduces the effective length of pipe

Using, f = n v / 4 Leff

n = 1

293.6 = 1 x 341 / 4 ( 0.36 - H)

H = 0.0696m

H = 6.96 cm

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