Apps-On-Physics/C3/Interference-and-Diffraction/English-timed

Time	Narration
00:01	Welcome to the Spoken Tutorial on Interference and Diffraction.
00:07	At the end of this tutorial you will be able to,
00:11	Verify the relation between wavelength and relative intensity.
00:16	Find the relation between slit width, maxima and minima.
00:21	Calculate the angle for the given maxima.
00:24	Interpret diffraction intensity profile.
00:28	Verify the relation between wavelength and angle.
00:33	Here I am using, Ubuntu Linux OS version 16.04, Firefox Web Browser version 62.0.3
00:46	To follow this tutorial, learner should be familiar with Apps on Physics.
00:52	For Pre-requisites tutorials please visit this site.
00:58	I have already downloaded Apps on Physics to my Downloads folder.
01:03	In this tutorial we will use, Interference of Light at a Double Slit and Diffraction of Light by a Single Slit Apps.
01:13	Right click on doubleslit_en.htm file.
01:18	Select the Open With Firefox web Browser option. App opens in the browser.
01:25	The App shows Young’s double slit experiment for the interference pattern.
01:32	The setup includes a slit and a semicircular screen.
01:39	On the green panel we can change the wavelength of the source light.
01:44	Here the range of the wavelength is from 380 nanometer to 780 nanometer. This is the range of visible spectrum.
01:56	We can also enter the value of wavelength in the text-box.
02:03	Let us see how change in wavelength changes the interference pattern.
02:09	Drag the Wavelength slider to 380 nanometer
02:14	Click on Intensity profile radio button at the bottom of the green panel.
02:20	Drag the Wavelength slider slowly towards higher wavelength.
02:25	Observe the graph showing dark and bright fringes in the intensity profile.
02:32	As the wavelength increases, distance between dark and bright fringes increases.
02:40	Next Drag the Angle slider here we can change the angle from 0 degrees to 90 degrees.
02:48	Note that as we change the angle, white arrows shifts their position.
02:55	This shift is also shown in the graph.
03:00	Scroll down the screen.
03:03	Here the conditions for maxima and minima are given.
03:08	For more details please read the additional material provided in this tutorial.
03:15	Press F5 key on the keyboard to reset the App.
03:20	Scroll up and increase the spacing between the slit to 2000 nanometer.
03:26	Now click on the Maxima drop down. Here we will see more options for the k value.
03:36	Click on the Minima drop down.
03:38	Note that the first minima is formed at 8.6 degrees.
03:44	Click on the second minima that is k=2.
03:49	The white arrows shift to the second minima in both screen and graph.
03:56	Here the Relative intensity changes to zero(0).
04:01	Zero indicates dark fringe.
04:05	The waves superimpose and are out of phase to give zero intensity. This is destructive interference.
04:15	Click on the Intensity profile radio button.
04:19	Here note that the red points indicate zero intensity.
04:25	Now click on Maxima drop down and select k=3.
04:32	The red point has shifted to the third peak.
04:36	The Relative intensity has changed to 1.
04:41	Here the waves superimpose to form a wave with maximum intensity.
04:48	This is constructive interference. This constructive interference results in a bright fringe.
04:56	Click on Interference pattern radio button at the bottom of the green panel.
05:03	Note that the interference graph shows equally spaced dark and bright fringes.
05:11	Therefore the value of relative intensity only shows 0 and 1.
05:18	Press F5 key on the keyboard to reset the App.
05:23	Let us calculate the value of angle for first maxima.
05:29	To do so we can rearrange the equation given in the interface α = sin-1(kλ/d)
05:41	Take the value of k as 1 since we have to calculate the angle for the first maxima.
05:49	Take the value of wavelength and spacing between slit as shown on interface.
05:56	Next substitute the values in the formula.
06:00	The calculated value of angle of first maxima is 36.86 degree.
06:09	Let us compare with the value shown in the App.
06:13	Click on the Maxima drop down and select k=1.
06:18	Observe that the value of the angle next to K=1 is 36.9 degrees.
06:27	The value is comparable with the calculated value.
06:32	As an Assignment Change the Spacing between slits to 3500 nm and Calculate the angle of fourth and fifth maxima.
06:45	Let us move on to the next App.
06:48	Follow the same steps as shown earlier while opening the App.
06:54	The Diffraction of Light by a Single Slit opens on the screen.
07:00	This App shows the setup of diffraction through a single slit experiment.
07:06	This set up is also known as Fraunhofer's Diffraction at a single slit.
07:12	scroll down to see the conditions for maxima and minima.
07:17	Scroll up and select Intensity profile radio button.
07:23	Observe that, only one central bright region is seen.
07:28	This intensity decreases as we move away from the center.
07:34	In the green panel, click on the Width of slit text-box and enter 3000 nanometer.
07:42	Observe that a number of alternate dark and bright fringes are formed
07:48	Now click on the Maxima drop down.
07:51	Observe that the central maxima is at 0 degrees.
07:57	It shows Relative intensity as 1. This is the maximum intensity.
08:04	From the Maxima drop down select k=1.
08:09	Here the Relative intensity decreases from 1 to 0.0472.
08:18	Again click on Maxima drop down and select k=2.
08:25	The Relative intensity decreases to 0.0165.
08:32	Know Click on the Minima drop down and select k =2
08:38	The value of Relative intensity is shown as 0.
08:43	Click on Minima drop down and select k=4.
08:49	Note that for every dark fringe the value of relative intensity will remain zero.
08:57	Here I have made the table to show the relative intensity for maxima and minima.
09:05	Observe the relative intensity for maxima.
09:08	The Relative intensity decreases as we move away from central region.
09:15	For each minima, we have seen that the value remains zero for the relative intensity.
09:23	Drag the Wavelength slider to its highest value that is to 780 nm. This is the region of red light.
09:34	Next click on Maxima drop down. Here we see four bright fringes.
09:41	Next drag the slider of Wavelength to its lowest value that is to 380 nanometer. This is the region of violet light.
09:53	Now click on the Maxima drop down.
09:56	Here we can see eight positions for bright fringes.
10:01	This happens because violet light refracts more than red light.
10:07	Hence we see more number of bright fringes for violet light.
10:13	Drag the Wavelength slider to 520 nm.
10:18	Click on Maxima drop down and select first bright fringe.
10:23	Here the first bright fringe is formed at an angle of 14.4 degrees.
10:31	Again drag the slider of Wavelength to 720 nanometer.
10:37	Click on the Maxima drop down and select K=1.
10:42	Here the first bright fringe is formed at an angle of 20.1 degrees.
10:49	Hence we conclude that if we increase the wavelength, angle also increases.
10:56	Scroll down the screen. This is shown in the formula.
11:02	Here, the angle is directly proportional to the wavelength.
11:07	As an assignment, Change the wavelength to 380 nm and width of slit to 5000 nm.
11:17	Use the table as shown earlier in this tutorial for your reference.
11:23	Tabulate the total number of maxima and minima.
11:28	For each maxima tabulate the value of relative intensity from the App. Explain the diffraction pattern
11:38	Differentiate between interference and diffraction patterns.
11:43	Let us summarize.
11:45	In this tutorial we have, Verified the relation between wavelength and relative intensity.
11:52	Found the relation between slit width, maxima and minima.
11:58	Calculated the angle for the given maxima.
12:03	Interpreted diffraction intensity profile.
12:07	Verified the relation between wavelength and angle.
12:12	These Apps are created by Walter-fendt and his team.
12:17	The video at the following link summarizes the Spoken Tutorial project. Please download and watch it.
12:25	The Spoken Tutorial Project team, conducts workshops and gives certificates. For more details, please write to us.
12:35	Please post your timed queries in this forum.
12:39	Spoken Tutorial Project is funded by MHRD, Government of India.
12:45	This is Himanshi Karwanje from IIT-Bombay. Thank you for joining.

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