A tube is open only at one end. A certain harmonic produced by the tube has a frequency of 450 Hz. The next higher harmonic has a frequency of 750 Hz. The speed of sound in air is 343 m/s.
(a) What is the integer n that describes the harmonic whose frequency is 450 Hz?
(b) What is the length of the tube?

Respuesta :

Answer: the correct answer is a) the interger is n= 3  

b)the length of the tube L= 0.57 m

Explanation:

For a tube that is open at one end, nth harmonic frequency is given by

fn=n(v/4L)

the next higher harmonic frequency is given by

fn+2=n+2(v/4L)

Now we have the ratio

fn+2/fn = (n+2)/n= 1+2/n

2/n= [(fn+2)/fn]-1  or

n= 2/{[(fn+2)/fn]-1}

(a) In the problem we have

fn = 450Hz and fn+2= 750Hz So,

n=2/[(750/450)-1]  =3

then the frequency of 450Hz  corresponds to n=3

b) then we have

450=3v/4L      so,     L= 3v/(4*450)   (3*343)/(4*450) = 0.57m

 

The formula for the fundamental frequency for an open tube at one end is :

F = nV/4L

n = 3 and L = 0.6m approximately

Given that a tube is open only at one end. And a certain harmonic produced by the tube has a frequency of 450 Hz. The next higher harmonic has a frequency of 750 Hz. The formula for the fundamental frequency for an open tube at one end is :

F = V/4L

That is, 1st harmonic = V/4L = F

2nd harmonic = 3V/4L = 3F

3rd harmonic = 5V/4L = 5F

The general formula can therefore be F = nV/4L

For the first harmonic in the question,

450 = 343n/4L

make 4L the subject of the formula

4L = 343n/450

The next higher harmonic will be

750 = 343(n + 2)/4L

make 4L the subject of the formula

4L = 343(n + 2)/ 750

Equate the two 4L

343n/450 = 343( n + 2)/750

cross multiply

257250n = 154350( n + 2 )

257250n = 154350n + 308700

collect the likes term

257250n - 154350n = 308700

102900n = 308700

n = 308700/102900

n = 3

Given that the speed of sound in air is 343 m/s, The length of the tube can be calculate by using the same formula.

F = nV/4L

450 = 3(343)/4L

4L = 1029/450

4L = 2.28

L = 2.28/4

L = 0.57 m

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