# Fundamental standing wave in Closed tube

1. Jan 18, 2007

### stylez03

1. The problem statement, all variables and given/known data
You blow across the open mouth of an empty test tube and produce the fundamental standing wave of the air column inside the test tube. The speed of sound in air is 344 m/s and the test tube acts as a stopped pipe.

If the length of the air column in the test tube is 14.0 cm, what is the frequency of this standing wave?

L = 0.14m
V = 344 m/s
Closed Tube

2. Relevant equations

Closed Tube Frequency = Fn = nVair / 4L

3. The attempt at a solution

F1 = 1*344 / 4*0.14 = 614khz

I thought this was the right answer, but the online program says it's incorrect.

2. Jan 19, 2007

### silver-rose

That's the standing wave...perhaps it's asking for a resonance frequency? Seeing that it's an online program...maybe it wants more SIG FIGS?

3. Jan 19, 2007

### Kurdt

Staff Emeritus

Is it really KHz?

4. Jan 19, 2007

### stylez03

Well the online program already had the units ready, which was khz. Should there be a conversion?

5. Jan 19, 2007

### Kurdt

Staff Emeritus
The calculation you have done gives an answer in Hz and if the online thing wants it in KHz the yes you will have to convert from Hz to KHz

6. Jan 19, 2007

### stylez03

Thanks Kurdt, that seemed to work. I hate the units in some of these problems, guess I should pay attention as well.

7. Jan 19, 2007

### Kurdt

Staff Emeritus
Yes units are very important. They've probably done that to make you think about them.