View source for PhET-Simulations-for-Physics/C2/Bending-Light/English-timed

{| border = 1
|'''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. 
[http://phet.colorado.edu/ 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 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 let's 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: 

1. Use optical instruments like prism and lens 

|- 
|12:19
|2. 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 
|-
|}