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, Reflection of light Refraction of light Dispersion of light. How reflection and refraction varies with different material media.
00:52	We will also learn to, Use optical instruments like prism and lens Measure intensity of light
01:02	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. http://phet.colorado.edu
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 coloured 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, Reflection of light Refraction of light Dispersion of light How reflection and refraction varies with different material media.
12:12	We have also learnt to, Use optical instruments like prism and lens
12:19	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

Contributors and Content Editors

Madhurig, PoojaMoolya, Sandhya.np14