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Found in: Page 506

### Fundamentals Of Physics

Book edition 10th Edition
Author(s) David Halliday
Pages 1328 pages
ISBN 9781118230718

# Question: Figure 17-30 shows a stretched string of length and pipes a,b, c, and d of lengthsL, 2L, L/2, andL/2, respectively. The string’s tension is adjusted until the speed of waves on the string equals the speed of sound waves in the air.Thefundamental mode of oscillationis then set up on the string. In which pipe will the sound produced by the string cause resonance, and what oscillation mode willthat sound set up?

The sound produced by the string will cause resonance in pipe D, and the fundamental mode of oscillation will be set up by the sound.

See the step by step solution

## Step 1: Given

1. The length of the pipe a is L
2. The length of the pipe b is 2L.
3. The length of the pipe c is$\frac{L}{2}$
4. The length of the pipe d is$\frac{L}{2}$
5. The speed of wave on the string equals to the speed of sound.
6. The fundamental mode of n = 1oscillation is set up on the string.

## Step 2: Determining the concept

By using the formula for resonant frequency f for the pipe in which one end is open and other is closed, and for the pipe in which both ends are open, find the corresponding frequencies in each pipe. Comparing these frequencies with the frequency of the string, find the pipe in which cause resonance by the sound produced by the string and the oscillation mode that the resonating sound will set up.

Formulae are as follow:

1. The resonant frequency for the pipe in which one end is open and other is closed is,

$f=\frac{nv}{4L}$

Where,

$n=1,3,5,\dots .$

1. The resonant frequency for the pipe in which both ends are open is,

$f=\frac{nv}{2L}$

Where,

$n=1,3,5,\dots .$

Where,

f is frequency, L is length and vis velocity.

## Step 3: Determiningin which pipe will the sound produced by the string cause resonance and the type of oscillation mode that the resonating sound will set up

The resonant frequency for the pipe in which one end is open and other is closed is given by,

$f=\frac{v}{\lambda }$

Where,v is the speed of sound and $\lambda$is the wavelength,

$\lambda =\frac{4L}{n}$

Where,L is the length of the pipe and $n=1,3,5,\dots .$

For fundamental mode n = 1

Therefore, the resonant frequency is given by,

$f=\frac{v}{4L}$

Also, the resonant frequency f for pipe in which both ends are open is given by,

$f=\frac{v}{\lambda }$

Where, v is the speed of sound and $\lambda$ is the wavelength,

$\lambda =\frac{2L}{n}$

where, L is the length of the pipe and $n=1,2,3,\dots .$

For fundamental mode, n = 1

Therefore, the resonant frequency is given by,

$f=\frac{v}{2L}$

Let,${f}_{a},{f}_{b},{f}_{c}and{f}_{d}$ and be the frequencies in pipe a, b, c and d respectively.

Pipe ain which one end is open and other is closed and L =L . So,

${f}_{a}=\frac{v}{4L}$

Similarly, for pipe b with L 2 L ,

${f}_{a}=\frac{v}{4\left(2L\right)}=\frac{v}{8L}$

For pipe c in which both ends are open and $L=\frac{L}{2},\phantom{\rule{0ex}{0ex}}{f}_{c}=\frac{v}{2\left(\frac{L}{2}\right)}\phantom{\rule{0ex}{0ex}}{f}_{c}=\frac{v}{L}$

For pipe d in which one end is open and the other is closed and $L=\frac{L}{2},\phantom{\rule{0ex}{0ex}}{f}_{d}=\frac{v}{4\left(\frac{L}{2}\right)}\phantom{\rule{0ex}{0ex}}{f}_{d}=\frac{v}{2L}$

Now, the frequency of string with length for fundamental mode is given by,

${f}_{s}=\frac{v}{2L}$

Where

$\lambda =2L$

Therefore,

${f}_{s}={f}_{d}$

Hence, the sound produced by the string will cause resonance in pipe D and the fundamental mode of oscillation n = 1 will be set up by the sound.

Thus, by using the formula for resonant frequency for the pipe in which one end is open and other is closed and for the pipe in which both ends are open, this question can be solved.