Monday 29 Nov

Target: Understanding Sound

Correct Free Response:

 

Must know this formula (but it is not on the sheet):                

****       Vstring = √ {(FTension) / (mass/Length)}    

 

 Journal:

1. The number of segments in the standing wave shown in the diagram above is ____

2. The number of nodes & antinodes in the standing wave shown in the diagram above is ____.

3. A standing wave is formed when ____.

a. a wave refracts due to changes in the properties of the medium.

b. a wave reflects off a canyon wall and is heard shortly after it is formed.

c. red, orange, and yellow wavelengths bend around suspended atmospheric particles.

d. two identical waves moving different directions along the same medium interfere (constructive & destructive).

 

 

 

 

 

 

 

 

 

Answer:

1. 8 segments

2. (8 nodes)(7 antinodes)

3. D

 

 

                             

 

 

 

 

 

 

 

 

 

 

1. Explain the number and location of antinodes & nodes of the fundamental freq (standing wave) in two resonating pipes (2.0 m), and the l’s of each to that of a string:

  • a. One is open at both ends
  • b. one is open at one end and closed at the other
  • c. string

 

 

 

 

  

 

            a. Open ended: It has two antinodes (always at open ends) and one node (in the middle). This means that the standing wave  is taking up ½ of the pipe (l = 2L).

                l = twice the length of the pipe or 4.0 m

                        frequency:  f1 = V/2L

 

            b. One end closed: It has one antinod (open end) and one node (closed end). This means that the standing wave is taking up 1/4 of the pipe (l = 4L).  l = four times the length of the pipe or 8.0 m

               frequency: f1 = V/4L

 

    c. String has two nodes (always at ends) and one antinode (in the middle). This means that the standing wave is taking up ½ of the string. (l = 2L).

                l = twice the length of the string or 4.0 m

                        frequency:  f1 = V/2L

    (String's  l is same as the open ended, but has 2 nodes)

 

 

 

 

2. Compare the intensity, frequency, amplitude, wavelength, velocity and pitch of a point source at a distance 3d and d from the source?

 

 

 

 

 

 

 

  •  Intensity decreases (live all radiation & fields of force) 1/r2 or 1/32 = 1/9th as much

  • Frequency of sound doesn’t change due to distance

  • Amplitude is intensity:  so is 1/9th as much

  •  l doesn’t change

  •  Velocity doesn’t change because of distance

  •  Pitch is frequency: so doesn’t change

 

 

 

3. Compare the frequency, velocity, l standing wave on a string to the sound wave generated by the string.

     

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  • Same Frequency, the string pushes the air (compression waves) at the same frequency of its vibration.

  • Velocity on a string is different (almost always) than the velocity in air (which is normally about 343 m/s). V on a string depends on mass per meter, tension, length, etc.

 

 

 

 
 

 

1. An unknown tuning fork is sounded along with a tuning fork whose frequency is 350 Hz and a beat frequency of 10 Hz is heard.  What is the frequency of the unknown tuning fork?

 

 

 

 

 

 

 

 

 

 

 

340 or 360 HZ

 

 

 

 

 

2. A person stands between two speakers driven by the same source.  Each speaker produces a tone with a frequency of 200 Hz on a day when the speed of sound is 330 m/s.  If a person is 1.65 m from one speaker, how far from the other speaker does the person sense Constructive & Destructive interference?

 

 

 

 

 

 

 

 

First find l:

     f = vl

 330 = 200l

      l =  1.65m

     

Constructive interference: (Where two waves crests or troughs meet). Location must be an even l apart (i.e., 3.3m, 4.95m, etc). The difference in distance between the two speakers from the observer.

 

Destructive interference: (Where a waves crest and trough meet). Location must be an ½l apart (i.e., 2.475m, 4.125m,  etc). The difference in distance between the two speakers from the observer.

 

 

 

3. What characteristic of the sound (Frequency, Amplitude, Wavelength, Period) as you move toward a speaker emitting a pure tone?

a. If you move slowly

b. If you move quickly

 

 

 

 

 

 

 

 

 

 

 

a.  Freq: (same), Amplitude: (up),  l: (same), T: (same)

b. Freq: (up), Amplitude: (up),  l: (shorter), T: (shorter)

 

 

 

 

4. What happens to the of a wave's velocity on a stretched string when the tension in a string is doubled?

 

 

 

 

 

 

 

 

 

 

 

V = √ T/ML

Increase by √2

 

 

 

 

 

 

 

 

5.  What happens if the string’s mass is doubled?

 

 

 

 

 

 

 

 

 

 

 

V = √ T/ML

    a. goes down by √1/2

                                       

 

 

 

 

6. A standing wave of 5 segments, is set on a string 10 meters long. a. What is the wavelength (l) this wave.

b. What is the wave length of the string’s fundamental frequency. c. The wave’s velocity (if the fundamental frequency is 15Hz)?  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a.       Two Segments = one l. Therefore, 2/5 of 10m   is 4.0m

b.        One segment = 10m. 1/2 l is 10m, therefore one l is 20.0m

c.        V = f l   à  V = (15)(20) = 300m/s

 

 7. An instrument plays a note and has the following Frequency Spectrum for that note: 200, 400, 600, 800… The instrument most likely would be:

               

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

        

 A string and/or a wind, open ended (both)

           

 

 8. In the Doppler affect for sound waves, factors that affect the frequency that the observer hears include?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I. The speed of the source

II. The speed of the observer

III Direction of either the observer/source

 

 

 

4. An unknown tuning fork is sounded along with a tuning fork whose frequency is 350 Hz and a beat frequency of 10 Hz is heard.  What is the frequency of the unknown tuning fork?

 

 

 

 

 

 

 

 

 

 

 

340 or 360 HZ