# Apps-On-Physics/C2/Reflection-and-Refraction/English

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 Visual Cue Narration Slide Number 1 Title slide Welcome to the Spoken Tutorial on Reflection and Refraction. Slide Number 2 Learning Objectives In this tutorial, we will learn to, Simulate reflection and refraction of a light ray. Calculate the angles of reflection and refraction. Change the medium and angle of incidence to verify Snell's Law. Slide Number 3 Learning Objectives Calculate the value of critical angle. Verify Huygens' principle. Slide Number 4 System Requirements Here I am using, Ubuntu Linux OS version 16.04 Firefox web browser version 62.0.3 Slide Number 5 Pre-requisites To follow this tutorial, learner should be familiar with Apps on Physics. For pre-requisites tutorials please visit this site. Slide Number 6 Link for Apps on physics. Use the given link to download the Apps. Open the Downloads folder. I have already downloaded the Apps on Physics to my Downloads folder. Slide Number 7 Apps on Physics In this tutorial, we will use, Refraction of Light and Reflection and Refraction of Light Waves Apps. Right-click on refraction_en.htm file. Select the option Open With Firefox web Browser option. Cursor on the App. Right-click on refraction_en.htm file. Select the option Open With Firefox web Browser. Reflection and Refraction of Light App opens in the browser. Cursor on the interface. The App shows reflection and refraction of light through a given medium. Point to air and water on the interface The default media are air and water. Point to air. Point to water. Note that the medium with lesser refractive index is shown in white background. The medium with greater refractive index is shown in blue background. Point to the light that has been incident. Light from the top left corner, strikes the boundary surface of the two media. Point to both reflection and refraction angles. It shows reflection and refraction. Point to blue angles. Reflection is shown by the blue coloured angle. Point to black and blue angles. Observe that the angle of incidence and reflection are the same. Point to the refraction. Here we see the refraction of light. Show the phenomena with the motion of the cursor. When light travels from rarer medium to denser medium, it bends towards normal. Cursor on the green panel. On the green panel we have a choice to change a few parameters. Point to the drop downs. Let us reverse the two media using the drop downs. Click on the first drop down and change the medium to water. Select water as the upper medium. Click on second drop down. Select air from the drop down. Select air as the lower medium. Move the cursor to show the movements Here the ray of light travels from denser to rarer medium. The ray bends away from the normal. Click on both drop down to show the material medium. Note that both the drop downs show the same material media. Point to each drop down. Below the drop down, we see two text fields. These are provided to enter the values of refractive indices. Enter the value 4 in the 1st index of refraction and show the change. Here we can also change the values manually between the range of 1 to 5. Click on F5 key on the keyboard. Press F5 key on the keyboard to refresh the App. Change the values from 0.1 degrees to 90 degrees and show the changes. Click on F5 key on the keyboard to refresh and show the default value. Next Angle of incidence can be changed from 0.1 degrees to 90 degrees. Press F5 key to see the default value. It shows 30 degrees. Point below the text fields. Below the text fields App shows the Angle of reflection and refraction. Point to the graph. Graph shows the angle of refraction with angle of incidence. Click and drag the angle of incidence. Drag it slowly. We can also change the angle of incidence by dragging this red coloured ray. Point and show the changes when the angle of incidence is changed. Notice the change in angle of reflection and refraction. Simultaneously observe the graph. Cursor on the interface. Now from the graph we will learn the two cases of Snell’s law. Slide Number 8 Snell’s Law of Refraction sin i / sin r = n21 “n21” is the refractive index of the second medium w.r.t first. Before that let us state Snell’s law of refraction. Ratio of sine of angle of incidence to sine of angle of refraction is a constant. n21 is the refractive index of second medium with respect to first medium. Slide Number 9 Snell’s Law of Refraction Case1: If n21 > 1, angle of refraction is less than angle of incidence. Case2: If n21 < 1, angle of refraction is greater than angle of incidence. Here are the 2 cases of Snell’s law. 1. If n21 is greater than 1, angle of refraction is less than angle of incidence. 2. If n21 is less than 1, angle of refraction is greater than angle of incidence. Edit the value of Angle of incidence to 20 degrees. Change the Angle of incidence to 20 degrees. Observe that the angle of refraction has changed to 14.9. Point to the graph and values of the angles. This graph shows the first case of Snell’s law. Here angle of incidence is greater than the angle of refraction. Point to the value of refractive index of the second medium. Observe that the light ray bends towards the normal. Cursor on the interface. Let us see what happens, when incident ray passes from denser to rarer medium. Click on the first drop down and change the medium to diamond. From the first drop down change the material medium to diamond. Point to show the refraction. Notice that the light ray has bent away from the normal. Point to the graph. This graph shows the second case of Snell’s law. Point to show Angle of refraction. Here the angle of refraction is greater than the angle of incidence. Change the Angle of incidence to 30 degrees. Increase the Angle of incidence to 30 degrees. Point to the refracted ray. The refracted ray has bent still more further away from the normal. Change the Angle of incidence to 35 degrees. Again increase the angle of incidence to 35 degrees. In this case observe that the refraction is not possible. Point to the reflected ray. Here the incident ray is totally reflected. Cursor on the interface. This phenomenon is known as total internal reflection. Here the critical angle is formed. Point to the Critical angle. The critical angle for diamond and water is 33.3 degrees. Slide Number 10 Critical angle ic= sin-1(n2/n1) ic= Critical angle n1= Refractive index of first medium n2= Refractive index of the second medium Now we will calculate the critical angle using the formula. Slide Number 11 Tabular column Let us make a tabular column to calculate critical angle for two different media. point to the calculated values. Here I have calculated the critical angle for diamond and water. Point to the on the interface Critical angle. The calculated value is comparable to the value shown in the App. Slide Number 12 Tabular column Now enter these values in the table. Change the upper medium to water and lower medium to air. Next change the upper medium to water and lower medium to air. Slide Number 13 Tabular Column Show one glimpse of the table Note the refractive indices for both the media. Show the calculation of critical angle as image. Then calculate the critical angle using the above formula. Point to show the values. Observe that the values are comparable. Slide Number 14 Tabular column Note these values in the table. Slide Number 15 Assignment Show the incomplete table. As an assignment Note the values of refractive indices for the following media from the App. Calculate the critical angle for the two media. Compare the values with the ones shown in the App. Cursor on the interface. Now we will move on to the next App. Right click on refractionhuygens_en.htm. Open With Firefox Web Browser. Right click on refractionhuygens_en.htm file. Open With Firefox Web Browser. The App opens in the browser. Highlight the main topic from the screen. App shows Reflection and Refraction of light waves using Huygen's principle. Click on the Restart button. Click on the Restart button. Point to the wavefront. Here the plane wavefront is incident diagonally on the boundary of the media. Click on the Next step button. Click on the Next step button. Point to the box and scroll the slider.(Highlight the box) Explanation of each step is provided in this text box. Point to the wavefronts. Note the change in media, when the wavefront is incident on the boundary. Click on the Pause button. Click on the Pause button. Point to the pink point on the boundary. Observe the pink points on the boundary between the media. Each pink point is the source of spherical wavefront. Point to the waves in Medium1 and Medium 2. These generating waves in the Medium 1 and Medium 2 are the wavelets. Click on the Resume button. Click on the Resume button. Cursor on the interface. Note that the waves in Medium 2 move with less velocity as compared to Medium 1. This is because, the medium 2 has higher refractive index. So here the waves move with less velocity. Click on the Next step button. Click on the Next step button. Click on the Pause button. Click on the Pause button. Point to the line drawn. Observe the tangent drawn to all these spherical waves. This line, here is the source of the secondary wavefront. Points on the wavelets. So, the points on every wavelet results in the formation of secondary wavefront. Point to the values. Here the values of Angle of incidence, reflection and refraction are given. Click on the Resume button. Click on the Resume button. Point and show the direction of propagation of the red and blue waves. Direction of propagation changes when waves move from medium 1 to medium 2. Click on the Next step button. Again click on the Next step button. Point to direction of the propagation of waves. Here the direction of the propagation of waves is shown. Click on the Pause button. Click on the Pause button. Point and show the perpendicular lines. Observe that these lines of propagation are perpendicular to the wavefronts. Click on the Resume button. Click on the Resume button. Change Angle of incidence = 60 degrees. Change the Angle of incidence to 60 degrees. Click on the Next step. Click on the Next step button. Point the series of waves. Here we can see a series of wavefronts that are incident on the boundary surface. Cursor on both mediums. Observe the speed and wavelength of wavefronts in both the media. Point to the denser medium. The wavelength and speed of the wavefront decreases in the denser medium. But the frequency of the plane wavefronts remains the same. make the refractive index of 1 to 2 and refractive index of 2 to 1. Let us reverse the refractive indices and observe the formation of wavefronts. Point to the wavefronts. Here the speed of the wavefront decreases, as it moves from denser medium. Cursor on the interface. Point to show the critical angle. This shows the total internal reflection. Here the incident wavefront is completely reflected and not refracted. This results in the formation of critical angle. Slide Number 16 Assignment Change the refractive index values of both media as given in Refraction of Light App. Observe the formation of wavefront and give an explanation. As an assignment Change the refractive index values of both media as given in Refraction of Light App. Observe the formation of wavefront and give an explanation. Let us summarize Slide Number 17 Summary Using these Apps, we have Simulated reflection and refraction of a light ray. Calculated the angles of reflection and refraction. Changed the medium and angle of incidence to verify Snell's Law. Slide Number 18 Summary Calculated the value of critical angle. Verified Huygens' principle. Slide Number 19 Acknowledgement These Apps are created by Walter-fendt and his team. These Apps were created by Walter-fendt and his team. Slide Number 20 About the Spoken Tutorial project. The video at the following link summarizes the Spoken Tutorial project. Please download and watch it. Slide Number 21 Spoken Tutorial workshops. The Spoken Tutorial Projectteam, conducts workshops and gives certificates. For more details, please write to us. Slide Number 22 Forum for specific questions: Do you have questions in THIS Spoken Tutorial? Please visit this site Choose the minute and second where you have the question. Explain your question briefly. Someone from our team will answer them. Please post your timed queries in this forum. Slide Number 23 Acknowledgement Spoken Tutorial Project is funded by MHRD Government of India. This is Himanshi Karwanje from IIT Bombay Thank you for joining.