Apps-On-Physics/C2/Sound-waves/English-timed
From Script | Spoken-Tutorial
| 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. |
