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

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.

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