Apps-On-Physics/C2/Reflection-and-Refraction/English-timed
From Script | Spoken-Tutorial
| Time | Narration |
| 00:01 | Welcome to the Spoken Tutorial on Reflection and Refraction. |
| 00:06 | In this tutorial, we will learn to,
Simulate reflection and refraction of a light ray. |
| 00:13 | Calculate the angles of reflection and refraction. |
| 00:17 | Change the medium and angle of incidence to verify Snell's Law. |
| 00:22 | Calculate the value of critical angle. |
| 00:26 | Verify Huygens' principle. |
| 00:29 | Here I am using,
Ubuntu Linux OS version 16.04 |
| 00:35 | Firefox web browser version 62.0.3 |
| 00:41 | To follow this tutorial, learner should be familiar with Apps on Physics. |
| 00:47 | For pre-requisites tutorials please visit this site. |
| 00:52 | Use the given link to download the Apps. |
| 00:56 | I have already downloaded the Apps on Physics to my Downloads folder. |
| 01:01 | In this tutorial, we will use,
Refraction of Light and Reflection and Refraction of Light Waves Apps. |
| 01:11 | Right-click on refraction_en.htm file. |
| 01:16 | Select the option Open With Firefox web Browser. |
| 01:21 | Reflection and Refraction of Light App opens in the browser. |
| 01:26 | The App shows reflection and refraction of light through a given medium. |
| 01:31 | The default media are air and water. |
| 01:36 | Note that the medium with lesser refractive index is shown in white background. |
| 01:42 | The medium with greater refractive index is shown in blue background. |
| 01:47 | Light from the top left corner, strikes the boundary surface of the two media. |
| 01:52 | It shows reflection and refraction. |
| 01:56 | Reflection is shown by the blue coloured angle. |
| 02:01 | Observe that the angle of incidence and reflection are the same. |
| 02:06 | Here we see the refraction of light. |
| 02:09 | When light travels from rarer medium to denser medium, it bends towards normal. |
| 02:16 | On the green panel we have a choice to change a few parameters. |
| 02:21 | Let us reverse the two media using the drop downs. |
| 02:26 | Select water as the upper medium. |
| 02:29 | Select air as the lower medium. |
| 02:33 | Here the ray of light travels from denser to rarer medium. |
| 02:38 | The ray bends away from the normal. |
| 02:42 | Note that both the drop downs show the same material media. |
| 02:48 | Below the drop down, we see two text fields.
These are provided to enter the values of refractive indices. |
| 02:48 | Here we can also change the values manually between the range of 1 to 5. |
| 03:05 | Press F5 key on the keyboard to refresh the App. |
| 03:10 | Next Angle of incidence can be changed from 0.1 degrees to 90 degrees. |
| 03:18 | Press F5 key to see the default value.
It shows 30 degrees. |
| 03:25 | Below the text fields App shows the Angle of reflection and refraction. |
| 03:31 | Graph shows the angle of refraction with angle of incidence. |
| 03:36 | We can also change the angle of incidence by dragging this red coloured ray. |
| 03:42 | Notice the change in angle of reflection and refraction. |
| 03:48 | Simultaneously observe the graph. |
| 03:51 | Now from the graph we will learn the two cases of Snell’s law. |
| 03:57 | Before that let us state Snell’s law of refraction. |
| 04:02 | Ratio of sine of angle of incidence to sine of angle of refraction is a constant. |
| 04:09 | n21 is the refractive index of second medium with respect to first medium. |
| 04:16 | Here are the 2 cases of Snell’s law. |
| 04:19 | If n21 is greater than 1, angle of refraction is less than angle of incidence. |
| 04:26 | If n21 is less than 1, angle of refraction is greater than angle of incidence. |
| 04:34 | Change the Angle of incidence to 20 degrees. |
| 04:38 | Observe that the angle of refraction has changed to 14.9. |
| 04:44 | This graph shows the first case of Snell’s law. |
| 04:48 | Here angle of incidence is greater than the angle of refraction. |
| 04:53 | Observe that the light ray bends towards the normal. |
| 04:58 | Let us see what happens, when incident ray passes from denser to rarer medium. |
| 05:04 | From the first drop down change the material medium to diamond. |
| 05:09 | Notice that the light ray has bent away from the normal. |
| 05:14 | This graph shows the second case of Snell’s law. |
| 05:18 | Here the angle of refraction is greater than the angle of incidence. |
| 05:23 | Increase the Angle of incidence to 30 degrees. |
| 05:27 | The refracted ray has bent still more further away from the normal. |
| 05:32 | Again increase the angle of incidence to 35 degrees. |
| 05:37 | In this case observe that the refraction is not possible. |
| 05:42 | Here the incident ray is totally reflected. |
| 05:46 | This phenomenon is known as total internal reflection. |
| 05:51 | Here the critical angle is formed. |
| 05:55 | The critical angle for diamond and water is 33.3 degrees. |
| 06:01 | Now we will calculate the critical angle using the formula. |
| 06:06 | Let us make a tabular column to calculate critical angle for two different media. |
| 06:13 | Here I have calculated the critical angle for diamond and water. |
| 06:18 | The calculated value is comparable to the value shown in the App. |
| 06:24 | Now enter these values in the table. |
| 06:28 | Next change the upper medium to water and lower medium to air. |
| 06:34 | Note the refractive indices for both the media. |
| 06:39 | Then calculate the critical angle using the above formula. |
| 06:44 | Observe that the values are comparable. |
| 06:48 | Note these values in the table. |
| 06:52 | As an assignment
Note the values of refractive indices for the following media from the App. |
| 07:00 | Calculate the critical angle for the two media.
Compare the values with the ones shown in the App. |
| 07:09 | Now we will move on to the next App. |
| 07:12 | Right click on refractionhuygens_en.htm file. |
| 07:18 | Open With Firefox Web Browser. |
| 07:22 | The App opens in the browser. |
| 07:25 | App shows Reflection and Refraction of light waves using Huygen's principle. |
| 07:31 | Click on the Restart button. |
| 07:34 | Here the plane wavefront is incident diagonally on the boundary of the media. |
| 07:40 | Click on the Next step button. |
| 07:44 | Explanation of each step is provided in this text box. |
| 07:49 | Note the change in media, when the wavefront is incident on the boundary. |
| 07:55 | Click on the Pause button. |
| 07:58 | Observe the pink points on the boundary between the media. |
| 08:03 | Each pink point is the source of spherical wavefront. |
| 08:08 | These generating waves in the Medium 1 and Medium 2 are the wavelets. |
| 08:14 | Click on the Resume button. |
| 08:17 | Note that the waves in Medium 2 move with less velocity as compared to Medium 1. |
| 08:25 | This is because, the medium 2 has higher refractive index.
So here the waves move with less velocity. |
| 08:35 | Click on the Next step button. |
| 08:39 | Click on the Pause button. |
| 08:42 | Observe the tangent drawn to all these spherical waves. |
| 08:47 | This line, here is the source of the secondary wavefront. |
| 08:52 | So, the points on every wavelet results in the formation of secondary wavefront. |
| 08:59 | Here the values of Angle of incidence, reflection and refraction are given. |
| 09:06 | Click on the Resume button. |
| 09:09 | Direction of propagation changes when waves move from medium 1 to medium 2. |
| 09:16 | Again click on the Next step button. |
| 09:20 | Here the direction of the propagation of waves is shown. |
| 09:25 | Click on the Pause button. |
| 09:28 | Observe that these lines of propagation are perpendicular to the wavefronts. |
| 09:35 | Click on the Resume button. |
| 09:38 | Change the Angle of incidence to 60 degrees. |
| 09:42 | Click on the Next step button. |
| 09:45 | Here we can see a series of wavefronts that are incident on the boundary surface. |
| 09:52 | Observe the speed and wavelength of wavefronts in both the media. |
| 09:58 | The wavelength and speed of the wavefront decreases in the denser medium. |
| 10:04 | But the frequency of the plane wavefronts remains the same. |
| 10:09 | Let us reverse the refractive indices and observe the formation of wavefronts. |
| 10:15 | Here the speed of the wavefront decreases, as it moves from denser medium. |
| 10:22 | This shows the total internal reflection. |
| 10:26 | Here the incident wavefront is completely reflected and not refracted.
This results in the formation of critical angle. |
| 10:37 | As an assignment
Change the refractive index values of both media as given in Refraction of Light App. |
| 10:46 | Observe the formation of wavefront and give an explanation. |
| 10:51 | Let us summarize |
| 10:53 | Using these Apps, we have Simulated reflection and refraction of a light ray. |
| 11:00 | Calculated the angles of reflection and refraction. |
| 11:05 | Changed the medium and angle of incidence to verify Snell's Law. |
| 11:10 | Calculated the value of critical angle.
Verified Huygens' principle. |
| 11:18 | These Apps were created by Walter-fendt and his team. |
| 11:23 | The video at the following link summarizes the Spoken Tutorial project.
Please download and watch it. |
| 11:31 | The Spoken Tutorial Projectteam, conducts workshops and gives certificates.
For more details, please write to us. |
| 11:41 | Please post your timed queries in this forum. |
| 11:46 | Spoken Tutorial Project is funded by MHRD Government of India. |
| 11:52 | This is Himanshi Karwanje from IIT Bombay
Thank you for joining. |
