PhET/C2/Color-Vision/English-timed

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Time Narration
00:01 Welcome to this tutorial on Color Vision, an interactive PhET simulation.
00:08 In this tutorial, we will demonstrate, Color Vision, an interactive PhET simulation.
00:17 Here I am using, Ubuntu Linux Operating System version 16.04
00:25 Java version 1.8.0
00:29 Firefox Web Browser version 60.0.2
00:35 Learners should be familiar with high school physics and biology.
00:41 Using this simulation, we will look at colour vision when the human eye sees:

White light

00:50 Light of different colours from the visible spectrum
00:55 Light and filters of different colours of the visible spectrum
01:00 Red, green and blue light, separately or in combination
01:06 Please refer to the additional material provided with this tutorial.

Let us begin.

01:14 Visible Light

A portion of the electromagnetic spectrum is detected by human eye as visible light.

01:25 This portion extends from 380 to 760 nanometers'.
01:33 The colours of the visible spectrum can be remembered as VIBGYOR.
01:39 Violet, indigo, blue, green, yellow, orange, red
01:47 The lowest wavelength (highest frequency) appears violet.
01:53 The highest wavelength (lowest frequency) appears red.
01:59 Combining all the colours gives white light.
02:04 Use the given link to download the simulation.
02:09 I have already downloaded the Color Vision simulation to my Downloads folder.
02:16 To open the simulation, right click on the color-vision_en.html file.
02:23 Select the Open With Firefox Web Browser option.

The file opens in the browser.

02:32 This is the interface for the Color Vision simulation.
02:37 Now we will explore the interface.
02:41 The interface has two screens

Single Bulb

RGB Bulbs

02:49 Click on Single Bulb screen.
02:53 In the Single Bulb screen, you can see a person facing the right.

Just below the neck are two small images.

03:04 The first one is highlighted.

It allows you to see the person’s face.

03:11 Click on the second image.

On being highlighted, it shows the cross-section of the person’s brain.

03:20 Observe the optic nerves extending from the eyes into different parts of the brain.
03:28 Color Vision,

Cone cells are photoreceptors in the retina that are sensitive to a range of wavelengths.

03:39 The leaf absorbs all wavelengths of visible light except green light.
03:46 Green light of 520 nanometers wavelength is reflected and reaches the eye.
03:54 Here, it activates the M or gamma type cones.
03:59 The visual information is sent from cones to retinal ganglia via the optic nerve.
04:07 The two optic nerves meet and cross over each other at the optic chiasma.
04:14 Now called optic tracts, they enter and synapse in the thalamus.
04:21 They then continue to the primary visual cortex in the occipital lobe in the back of the brain.
04:30 Let us return to the simulation.
04:34 Observe the ellipses above the person’s head.
04:39 They will be filled with the colour that the person sees.
04:44 Note the Play/Pause button at the bottom and the Step button next to it.
04:51 The Reset button will take us back to the start.
04:55 Observe the torch or flashlight in front of the person’s eyes.
05:01 The red button on the flashlight will switch it off and on.
05:06 Click on the first bulb above the flashlight.
05:11 This is white light.

Click on the red button of the flashlight.

05:18 The first image below the flashlight is highlighted by default.
05:24 This will show the light as a beam.
05:28 Click on the second image below the flashlight.
05:33 This will show the light in the form of photons.
05:38 Click on the Pause button.

Observe that the Step button is active.

05:45 Click on the Step button to see the photons move in a stepwise manner.
05:51 Click on the first image to return to the beam from the flashlight.
05:57 Observe the white ellipses above the person’s head.
06:02 This means that the person sees white light coming out of the flashlight.
06:08 Click on the second bulb above the flashlight.

Observe the slider Bulb Color containing all colours of the visible spectrum.

06:19 Drag the Bulb Color slider from end to end.
06:24 The colour on which the handle is placed indicates the colour of the light from the flashlight.
06:31 Observe that the ellipses above the person’s head fill with the same colour.
06:38 You can change the colour that the person sees by dragging the Bulb Color slider.

Drag the Bulb Color slider to red at the right end.

06:50 Note that there is a toggle switch in front of the person.

It is connected to the Filter Color slider.

06:59 Observe that the Filter Color slider also contains the colours of the visible spectrum.
07:06 Click on the toggle switch.

Observe that a filter appears in the path of the beam from the flashlight.

07:16 Drag the Filter Color slider from end to end.
07:21 The colour on which the handle is placed indicates the colour of the filter.
07:28 Note the filter is red and transmits a red beam.

The person also sees red light.

07:38 Drag the Bulb Color slider to violet.

Violet light comes out from the flashlight.

07:56 But with red as the Filter Color, no light is transmitted to the person.
07:52 The person does not see any light.
07:56 Drag the Filter Color slider to violet at the left end.
08:02 Note the filter becomes violet and violet light is transmitted to the person.

The person now sees violet light.

08:13 Drag the Bulb Color slider to red at the right end.
08:19 Observe how the filter remains violet but the light beam is now red.
08:26 But the violet filter does not transmit the red light.

The person sees no light.

08:35 Drag both sliders to different colours to see whether light is transmitted to the person.
08:43 Observe how light is only transmitted when both sliders are set at the same or nearly same colour.
08:53 The filter subtracts all wavelengths and only transmits the wavelength of its own colour.
09:01 Transmission is weaker for wavelengths very close to and maximum for the filter’s colour.
09:09 As an assignment, Choose white light to come from the flashlight and observe the transmission of light from the filter.
09:22 Now, let us click on the RGB Bulbs screen at the bottom of the interface.
09:29 Here, too, you can see the person facing the right.

Click on the second image which allows you to see the cross-section of the person’s brain.

09:41 The Play/Pause, Step and Reset buttons are all seen at the bottom of the interface.
09:49 Three sliders and three flashlights are seen on the screen.

All sliders are set at the minimum levels.

10:00 The uppermost one is a red slider, the second green and the lowermost one is a blue slider.
10:10 Drag the red slider to the maximum level.
10:15 Note how red photons come out of the flashlight next to the red slider.
10:22 The photons reach the person’s eye and the person sees red light.
10:28 Drag the green slider to the maximum level.

Note how red and green photons come out of the flashlights next to the red and green sliders.

10:41 Red and green add to give yellow.

The cones sensitive to red and green light are activated so that the person sees yellow.

10:53 Click the Pause button.
10:56 Drag the blue slider to the maximum level.
11:00 Click on Play button. Observe how all three colours mix so that the person sees white light.
11:11 Let us summarize.
11:14 In this tutorial, we have demonstrated how to use the Color Vision PhET simulation.
11:22 Using this simulation, we looked at colour vision when the human eye sees:

White light

11:31 Light of different colours from the visible spectrum
11:35 Light and filters for different colours of the visible spectrum
11:40 Red, green and blue light, separately or in combination
11:46 As an assignment,Adjust the red, blue and green sliders to get these 6 colours.
11:55 Which RGB combination would you pick to design these schemes?
12:01 Look for an image of the colour wheel on the Internet.
12:06 Pick colour combinations for the following schemes.
12:11 The video at the following link summarizes the Spoken Tutorial project.

Please download and watch it.

12:20 The Spoken Tutorial Project team conducts workshops using spoken tutorials and gives certificates on passing online tests.

For more details, please write to us.

12:35 Please post your timed queries in this forum.
12:40 This project is partially funded by Pandit Madan Mohan Malaviya National Mission on Teachers and Teaching.
12:49 Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.

More information on this mission is available at this link.

13:03 This is Vidhya Iyer from IIT Bombay, signing off.

Thank you for joining.

Contributors and Content Editors

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