Apps-On-Physics/C2/Sound-waves/English-timed

From Script | Spoken-Tutorial
Jump to: navigation, search
Time Narration
00:01 Welcome to the spoken tutorial on Sound Waves.
00:05 In this tutorial we will,

Form a standing wave.

00:10 Form nodes and antinodes.
00:14 View various types of harmonics of a standing wave.
00:19 Calculate the wavelength and frequency of standing waves.
00:24 Here I am using,

Ubuntu Linux OS version 16.04

00:30 Firefox web browser version 62.0.3
00:35 To follow this tutorial learner should be familiar with Apps on Physics.
00:41 For the pre-requisite tutorials please visit this site.
00:46 Use the given link to download the Apps.
00:50 I have downloaded the Apps to my Downloads folder.
00:55 In this tutorial we will use,

Standing Wave and Standing Longitudinal Waves Apps.

01:04 Right-click on standingwavereflection_en.htm file.
01:10 Select the option Open with Firefox Web Browser.
01:15 Standing Wave App opens in the browser.
01:19 In the green panel under Reflection we have two radio buttons.

from a fixed end and from a free end.

01:29 By default Reflection from a fixed end is selected.
01:34 Below these radio buttons you can see, Reset and Start buttons.
01:39 Start button is a toggle for Start, Pause and Resume.
01:44 At the bottom of the green panel you can see

Incidenting wave, Reflected wave and Resultant standing wave check-boxes.

01:54 These check-boxes are selected by default.
01:58 Click on the Start button.
02:01 On the yellow panel, observe the propagation of a wave in a string.
02:06 The red wave is the Incidenting wave.
02:10 The blue wave is the Reflected wave.
02:13 Observe that the reflected wave has a phase change of 180 degrees.
02:19 Here the incident and reflected waves have the same amplitude.
02:24 Let us uncheck the Reflected wave.
02:27 If we uncheck any of the check-boxes, we cannot see the corresponding wave.
02:33 Click the Reflected wave check-box to make it visible again.
02:37 Click on the Pause button to stop the propagation of the waves.
02:42 Here is the resultant standing wave.
02:45 This wave is formed due to the superposition of incident and reflected waves.
02:51 The resultant wave is the constructive superposition of the waves.
02:56 Now I will show the superposition of waves in a step-by-step manner.
03:01 Click on the Single steps radio button to show the animation step-by-step.
03:07 Here a drop down to show various time periods is seen.
03:13 By default it is T by 8.

We will leave it as it is.

03:19 Now click the Resume button three times to show different superpositions.
03:25 This is destructive interference of sound waves.
03:29 Here the waves are out of phase.

So they subtract each other and form a straight line.

03:37 Click on Resume button again.
03:40 This is an intermediate superposition of waves.
03:44 It lies between the constructive and destructive superpositions.
03:49 Again click on the Resume button.
03:52 This is constructive interference of the waves.
03:56 This is the amplitude of the resulting standing wave.
04:00 It is the sum of incident and reflected waves.
04:04 For the time period T by 8, one cycle takes three steps to complete.
04:10 T by 8 means 1/8th of the total time period.
04:16 Let us select T by 24 from the drop-down.
04:21 Click on the Resume button continuously to see various superpositions.
04:27 Observe that one superposition cycle now takes five steps.
04:33 You can try other options given in the drop-down on your own.
04:38 After the reflection from the fixed end, you can see A and N on the string.
04:45 Here N is a Node and A is an Antinode.
04:50 Let us define a Node and an Antinode.
04:54 Node is the point where the particles do not have any motion.
04:59 Antinode is the point where the particle oscillates with maximum amplitude.
05:06 As an assignment

Using Reflection from free end option, show the formation of standing waves.

05:15 Observe the reflection by selecting various time period options.

Explain your observation.

05:23 Let us move on to Standing longitudinal wave App.
05:27 To open the App right-click on standinglongitudinalwaves_en.htm file.
05:35 Select the option Open with Firefox Web Browser.
05:39 The App opens in the browser.
05:42 Here is the information related to the App interface.
05:47 Scroll down to see the interface completely.
05:51 This interface shows a tube filled with air molecules.
05:57 The blue dots inside the tube represent the air molecules.
06:03 Here we can see two plots.
06:06 Displacement of particles and Divergence from average pressure.
06:12 X axis represents the length of the tube.
06:16 Δ(delta)x is the change in displacement of molecules from the equilibrium position.
06:22 Δ(delta)p is the Divergence from average pressure.
06:26 Observe the pink and red waves.
06:30 They show the instantaneous movement of air molecules.
06:35 In the green panel, under the heading Form of tube, we have three radio buttons.
06:42 By default both sides open radio button is selected.
06:47 Next, under Vibrational mode we see two buttons, Lower and Higher.
06:54 By default, the App shows the lowest Vibrational mode.
06:59 The lowest vibrational mode of the system is known as fundamental.
07:04 Fundamental vibrational mode is the first harmonic followed by higher harmonics.
07:10 We can change the Length of the tube in this box.
07:14 Length of the tube can be varied between 1 meter to 10 meters.
07:20 The App calculates the Wavelength and Frequency based on the length of the tube.
07:26 Click the Higher button continuously.

It shows 5 overtones for the six harmonical vibrations.

07:34 Press F5 key on the keyboard to reset the App.
07:39 Observe the motion of air molecules.
07:43 Molecules in the middle of the tube do not displace from the mean position.
07:49 Therefore in the Displacement of particles graph, node is in the middle.
07:55 Observe that particles at the extreme positions are oscillating in and out.
08:02 Here particles oscillate with maximum amplitude.
08:07 Therefore antinode is present at the extreme ends of the X- axis.
08:13 Let us move to the second graph.
08:16 Observe the movement of particles inside the tube and graph simultaneously.
08:22 In the graph, movement of the pink wave shows the changes in the pressure.
08:28 As the particles move towards the center, they get compressed.

So pressure increases.

08:35 When they move away pressure decreases.
08:39 Under Form of tube, select one side open radio button.
08:45 Observe the movement of particles in this form of the tube.
.08:49 Here particles at the closed end are not moving.

Therefore the pressure is maximum at this end.

08:58 Let us calculate the wavelength in this form of the tube.
09:03 First let us define wavelength.
09:06 Wavelength is the distance between two consecutive peaks.
09:10 Click on the Higher button to show the first overtone.
09:14 We have to calculate the wavelength of first overtone wave.
09:19 Mathematically we can write, L = n by 4 of lambda
09:25 There L is length of the tube and lambda is the wavelength.

n’ can take values from 1 to n.

09:34 By rearranging the equation we can write this as

lambda= 4L upon n

09:41 Let us calculate the wavelength.
09:44 The wavelength of the first overtone is three-fourth of the complete wave.

Here the value of n is 3.

09:54 From the App, value of length of tube can be taken as L.
09:59 Therefore the calculated value of wavelength is 1.33 metre.
10:05 This is the wavelength of first overtone mode of vibration.
10:10 Now we will calculate the frequency of the wave.
10:14 The number of complete oscillations per second is the frequency of a sound wave.
10:21 It is measured in hertz (Hz).
10:24 Frequency is calculated using the formula.

f=c/λ (f is equal to c upon lambda)

10:31 λ (lambda) is wavelength and c is speed of sound wave
10:37 The App shows the value of speed of sound wave as 343.5 metre per second at 20 degree Celsius.
10:48 Let us calculate the frequency of the same wave.
10:51 Substitute the values for the above formula from the App.
10:57 The value for the frequency is 258.27 Hertz.
11:03 This value is comparable to the value shown in the App.
11:07 Make a tabular column to show the wavelength and frequency for 6 harmonical modes.
11:15 Click on the Higher button to go to next harmonic.
11:19 Similarly I have calculated frequency and wavelength for higher harmonics.
11:27 As an assignment, Change the length of tube to 8 metre.
11:33 Calculate the wavelength and frequency for different vibrational modes.
11:38 Another assignment.

Change the form of tube to both sides closed and explain the graphs.

11:46 Let us summarize.
11:48 Using these Apps we have,

Formed a standing wave.

11:55 Formed nodes and antinodes.
11:59 Viewed various types of harmonics of a standing wave.
12:04 Calculated the wavelength and frequency of standing waves.
12:09 These Apps were created by Walter-fendt and his team.
12:13 The video at the following link summarizes the Spoken Tutorial project.

Please download and watch it.

12:21 The Spoken Tutorial Project team conducts workshops and gives certificates.

For more details, please write to us.

12:31 Please post your timed queries on this forum.
12:35 Spoken Tutorial Project is funded by MHRD, Government of India.
12:41 This is Himanshi Karwanje from IIT-Bombay.

Thank you for joining.

Contributors and Content Editors

PoojaMoolya