PhET/C2/Bending-Light/English-timed
| Time | Narration |
| 00:01 | Welcome to this tutorial on Bending Light, an interactive PhET simulation. |
| 00:07 | In this tutorial, we will learn how to use Bending Light, interactive PhET simulation. |
| 00:14 | To follow this tutorial, learners should be familiar with topics in high school science. |
| 00:21 | Here I am using -
Ubuntu Linux OS version 14.04 Java version 1.7.0 Firefox Web Browser version 53.02.2. |
| 00:37 | Using this simulation, we will learn:
1. Reflection of light 2. Refraction of light 3. Dispersion of light 4. How reflection and refraction vary with different material media. |
| 00:52 | We will also learn to,
1. Use optical instruments like prism and lens 2. Measure intensity of light |
| 01:02 | 3. Measure velocity of light and view different wave patterns. |
| 01:08 | Let’s define reflection, refraction and dispersion. |
| 01:14 | Reflection, is bouncing back of a light ray after hitting any surface.
For example- A mirror reflects the image of the observer. |
| 01:26 | Refraction, is bending of a light ray when it enters a medium. |
| 01:32 | Light changes its speed and angle of propagation as it enters a different medium.
For Example: Bending image of a pencil in a beaker of water. |
| 01:45 | Dispersion, is a process of splitting of white light into seven colours. |
| 01:51 | For Example, formation of a rainbow on a cloudy day. |
| 01:57 | So, let's begin. |
| 01:59 | Use the given link to download the simulation. |
| 02:03 | I have already downloaded Bending light simulation to my Downloads folder. |
| 02:09 | To open the simulation, right-click on bending-light_en.html file. |
| 02:14 | Select Open With Firefox Web Browser option.
File opens in the browser. |
| 02:23 | This is the interface for Bending Light simulation. |
| 02:28 | The interface has three screens- Intro, Prisms and More Tools. |
| 02:35 | Let us begin our simulation with Intro screen.
Click on Intro screen to open it. |
| 02:42 | This screen has Ray and Wave radio buttons on the top left corner,
a movable laser pointer to turn on the laser light. |
| 02:53 | We can see green colored arrows when mouse pointer is placed on the laser.
These arrows show the direction in which the laser moves. |
| 03:06 | Click and drag the laser to move it from zero to 90 degrees.
Let us bring the laser to its default position. |
| 03:16 | Now let’s move onto the tools at the bottom left. |
| 03:21 | Here we see a tool box.
It consists of a protractor to measure angles, Intensity tool to measure intensity of light. |
| 03:32 | Below the tool box, we have a check-box to show Normal.
A Reset button is provided at the right hand side corner, to reset the simulation. |
| 03:44 | Let us begin the simulation. |
| 03:47 | We can focus light in the form of a Ray , or a Wave depending on what we choose. |
| 03:54 | By default Ray is selected.
To turn on the laser, click the red button on the laser pointer. |
| 04:03 | Notice that laser light gets reflected and refracted. |
| 04:09 | Observe that as we drag the laser pointer, angle of reflection and refraction changes. |
| 04:17 | Let’s use the protractor tool to measure angle of incidence refraction and reflection. |
| 04:25 | Place the protractor at the intersection point of incident ray, normal, refracted and reflected rays. |
| 04:35 | Observe that angle of incidence is equal to angle of reflection.
Drag the protractor back to its place. |
| 04:44 | Next we will move on to right hand side of the Intro screen. |
| 04:50 | Here, we have controls to measure refractive index in both the media. |
| 04:56 | There is a slider to change the material medium, or buttons to click. Initially, the slider is near Air. |
| 05:07 | As we drag the slider, medium changes from Air to Water and then to Glass. |
| 05:15 | When medium is changed, the angle of refraction changes. Index of Refraction(n) also changes. |
| 05:24 | We can see the changing value in the box. Drag the slider back to Air in the upper medium. |
| 05:32 | By default slider is on Water in the lower medium.
Drag the slider and place it between Water and Glass in the lower medium. |
| 05:44 | Now lets measure, the intensity of light using Intensity tool. |
| 05:49 | Click and drag the Intensity tool to the medium. |
| 05:53 | Intensity tool consists of a magnifier and a meter to measure intensity of light. |
| 06:00 | I will place the magnifier on the incident light. Meter shows 100% intensity. |
| 06:08 | Now drag and place the magnifier on refracted light. Meter shows value as 86.08%.
Intensity decreases because it depends on the medium. |
| 06:24 | As we drag the medium slider, value on the intensity meter changes.
This is because angle of refraction changes. |
| 06:34 | Similarly place the magnifier on reflected light. Meter shows value as 13.55%. |
| 06:44 | You can drag the slider to see a different value of intensity. |
| 06:51 | Now, change Ray to Wave and observe the bending of light. |
| 06:56 | Now we will move on to Prisms screen. |
| 07:00 | Click on Prisms screen, at the bottom of the interface. |
| 07:06 | In this screen we have the following tools-
Slider to change the environment, Monochromatic ray, |
| 07:15 | Monochromatic beam, white light, slider to change wavelength of light. |
| 07:22 | At the bottom of the screen we have-
prisms and lenses |
| 07:29 | Slider to change the Objects.
Check boxes for Reflections, Normal and Protractor. Reset button is at the right hand-side bottom corner. |
| 07:43 | laser has a screw provided at its end. Direction of laser can be changed using this screw. |
| 07:52 | Here arrows indicate direction of motion. laser can be moved up and down. |
| 08:00 | Now let’s begin the simulation. |
| 08:03 | Click on monochromatic beam. Click on the laser light. |
| 08:09 | Click on Reflections check box to see multiple reflections. |
| 08:14 | Place a prism in the path of light. You can see bending of light. |
| 08:21 | Move the wavelength slider gradually from red to violet.
Notice the bending of light as wavelength changes. |
| 08:32 | Prism is provided with a screw at its corner. |
| 08:38 | Drag the screw to change the direction of the prism.
As we change the direction notice the bending of light. |
| 08:47 | As an assignment
Change prism to glass slabs and observe the bending of light. |
| 08:54 | Now will see dispersion of light using white light. |
| 08:59 | Click on white light tool. Observe the dispersion of light. |
| 09:05 | Drag the Objects medium slider and observe the dispersion of light. |
| 09:11 | Place a lens in the path of dispersed beam of light.
The dispersed beam of light shows multiple reflections. |
| 09:26 | As an assignment
Use various lenses and observe the dispersion. |
| 09:32 | Change various Environments and observe the dispersion. |
| 09:37 | Now we move on to More Tools screen. |
| 09:41 | Click on More Tools screen.
More Tools screen has a combination of tools from Intro and Prisms screens. |
| 09:51 | Tool box at the bottom has two additional tools:
Speed and Time. At the bottom we also have Angles check box. Click on the Angles check box. |
| 10:04 | Now we will change the laser light to Wave.
Additionally radio buttons- Normal and Slow Motion Also, Play/Pause and Forward buttons appear. |
| 10:18 | let’s begin the simulation. |
| 10:21 | Turn on the laser light. |
| 10:23 | Click on red button to turn on the laser pointer. let’s use the Time tool. |
| 10:31 | Drag and place the Time tool in the medium. Time tool has two magnifiers and a Meter. |
| 10:39 | Place one of the magnifiers on incident wave and observe the wave pattern.
Now place the other magnifier on the refracted wave. |
| 10:51 | Observe the wave pattern. It shows a phase shift. |
| 10:56 | Place the magnifier on the reflected wave.
Observe that, the new wave pattern is with reduced amplitude. |
| 11:06 | This is because, the reflected wave has much lower intensity. |
| 11:12 | Drag and place the Speed tool on the refracted wave.
The speed is 0.67 c. Here c is velocity of light equal to 3x10^8 m/s. Value of speed decreases, |
| 11:33 | This is because velocity of light decreases in a material medium. |
| 11:39 | As an assignment,
Change material medium and notice the change in speed and wave pattern. |
| 11:48 | In this tutorial we have learnt,
How to use Bending Light, interactive PhET simulation. |
| 11:57 | Using this simulation we have learnt,
1. Reflection of light 2. Refraction of light 3. Dispersion of light 4. How reflection and refraction varies with different material media. |
| 12:12 | We have also learnt to,
5. Use optical instruments like prism and lens |
| 12:19 | 6. Measure intensity of light Measure velocity of light and View different wave patterns. |
| 12:29 | The video at the following link summarizes the Spoken Tutorial project. Please download and watch it. |
| 12:36 | The Spoken Tutorial Project team, conducts workshops using spoken tutorials and gives certificates on passing online tests. |
| 12:46 | For more details, please write to us. Please post your timed queries on this forum. |
| 12:54 | This project is partially funded by, Pandit Madan Mohan Malaviya National Mission on Teachers and Teaching. |
| 13:03 | Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India. More information on this mission is available at this link. |
| 13:17 | This is Madhuri Ganapathi from IIT-Bombay signing off. Thank you for joining |
