LAB 4: Exploring Reflection and Refraction with Virtual Ray Tracing

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Apr 3, 2024

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Physics LAB 4: Ray Tracing, Laws of refraction and Snell’s Law using a Virtual Setup: Virtual Lab Group 1 Name: Sahiry Alanis, Karla Duran, Eduardo Chavez, Jocelyn-Ambriz Hernandez Introduction: Background on Normal, Incident angle, reflected and Refracted ray : When light strikes an interface, some of the light bounces off the surface, and some will enter the glass. The light that bounces off the surface is said to have been “reflected”, or to have undergone reflection. The light that enters the glass is said to have been “refracted”, or to have undergone refraction. When we examine the properties of transparent medium like glass, it is important to first realize that glass work on the principle of reflection/refraction and that lenses (and prisms) work on the principle of refraction. Where mirror works on the principle of reflection only. Lenses and mirrors are often used to magnify or reduce images. To do this the light will be either focused to a real focal point (like in a concave mirror or a converging lens) or spread away from a virtual focal point (like in a convex mirror or a diverging lens). At first, we will be working on to verify the laws of reflection. Figure: Reflection and refraction of light at the interface of air and glass Activity 1 : Go to this is the link : https://phet.colorado.edu/en/simulation/bending-light When the site opens, scroll down until you see a light blue circle with PHYICS inside. Click this circle. Then select Light & Radiation. Next, find the App called “Bending of Light.” Finally, click on the app (you may click on the Play button or the Red 5) You will start the lab using the Intro section. Preliminary Investigation [turn over]

1. Turn the laser on by clicking the red button. You will see light getting reflected and refracted, but you will be focusing only on reflected ray for this part of the experiment. Now move the laser pointer left and right to change the angle of incidence as shown in figure and verify the laws of reflection. Incident Angle (Degrees)= Reflected Angles (Degrees) 15 20 30 45 45 75 60 85 2. What are some observations you make on angle of reflection when you change the angle of incidence? Describe them, ( answer, explain, evidence). the angle of incidence is changing on the measurement, the angle of reflection is moving towards the angle of incidence when moved to 90 degrees, but as the angle is moved away and to the centred of 0, the reflections go back to zero 3. What are the laws of reflections? Do you think, laws of reflection hold in your experiment? if it holds describe, ( answer, explain, evidence). The laws of Reflection are the rays of light that shows on a smooth surface. An example would be the angle of reflection which refers to the angle of incidence. Diffuse reflection is also shown, it helps reflect light in all areas of instead of just focusing on just one area. The law of reflection is shown in the experiment, due to us using the angle of incidence to capture the angle of reflection using the laser beam Activity 2 : Go to this is the link : https://phet.colorado.edu/en/simulation/bending-light When the site opens, scroll down until you see a light blue circle with PHYICS inside. Click this circle. Then select Light & Radiation. Next, find the App called “Bending of Light.” Finally, click on the app (you may click on the Play button or the Red 5) You will start the lab using the Intro section. Preliminary Investigation 4. Turn the laser on by clicking the red button. You will see light getting reflected and refracted. Now move the laser pointer left and right by clicking and holding on the silver part and moving it. What are some observations you make? Describe them, ( answer, explain, evidence). when the laser is moved to the left the angle reflection increases which makes the reflected ray be far away from the normal line and the angle of refraction increases as well which makes the refracted ray be far from the normal line as well. JDC – Created 05/02/2019 – Printed 20/02/2024

5. Now, leaving the pointer at about 45° change the material the pointer is in. It is currently in Air. Click the tab and try several other materials. What are some of your observations? ( answer, explain, evidence). When different materials are tried for the upper medium it is observed that the different trials produce the same reflection but different refraction of the laser. When the water is tried nothing happens glass the light bends more away from the normal line when mister A is tried there is a reflection but no refraction. When mystery B is tried there is no reflection or refraction. 6. Put the initial material back to Air. Now click on water in the lower material. Change it to several other materials and made record your observations. Is there are way to make the light, go straight from AIR into the lower material, ( answer, explain, evidence). PART I 1. For this part of the lab you will stay in the intro section. 2. Keep the starting material AIR, and the lower material WATER. 3. Drag the yellow protractor onto the experimental area. Move it so the AIR/WATER barrier line is just on 90°. The dotted Normal line must be at 0°. 4. Now you will change the incident angle to the angles listed on the table below. Use the protractor to set the Incident angle and find the Refracted angle. Incident Angle (Degrees)= Refracted Angles (Degrees) 0 0 15 11 30 22 JDC – Created 05/02/2019 – Printed 20/02/2024

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45 32 60 41 75 47 90 90 5. Using Snell’s law pick three incident angle and check to see if you PHET gave you the correct refracted angles. Show must your work . n 1sin θ 1 = n 2 sin θ 2 ,You willbe solvingfor θ 2 6. If you repeat the same experiment with “Glass” which has a higher index of refraction than water (air was less than water). How did this change the way the Laser Light bent? Light is refracted at a wider angle Note: For all of the angles you got a reflected ray (in air and for glass), for glass however, there were no Refracted rays for either 75° or 90°. This is due to Total Internal Refraction. Total Internal Refraction occurs when light goes from something Thick to something Thin at some bigger angles. As you increase the angle, you get to a point where the light bends so much that it can’t escape the material. This is Total Internal Reflection. The reflection you see at the lower angles is just Internal Reflection. It is not total because some light refracts, and some reflects. The initial angle where Total Internal Reflection occurs is called the critical angle. For light going from Glass to Water it must be somewhere between 60° and 75°. Activity 3 : Investigating critical angle and Total Internal Reflection using a PhET simulation Step 1 Go to https://phet.colorado.edu/en/simulation/bending-light , click on the button. Choose ‘Intro’ and set it up so that it looks like the screenshot below. The material in the top half should be water , the material in the bottom half should be air , and the angle of incidence should be about 30°. JDC – Created 05/02/2019 – Printed 20/02/2024

Step 2 Gradually increase the angle of incidence until i = 40°. The cropped screenshot on the right should help. Read off and record the angles of reflection and refraction below . Angle of reflection = …… 40 …………… ° Angle of refraction = ………… 55 ……… ° Step 3 Keep increasing the angle of incidence until the angle of refraction is as close to 90° as you can get it. (See the cropped screenshot on the right) If you increase the angle of incidence further then the refracted ray will disappear. The angle when this happens is called the “ critical angle ” for water. Record the critical angle for water here : Critical angle for water = 49° Step 4 JDC – Created 05/02/2019 – Printed 20/02/2024

Return the angle of incidence to 0° and change the material in the top half to glass. Repeat step 3 to find the critical angle for glass. Record it here : Critical angle for glass = 55° Step 5 Repeat the process to find the critical angle for material Mystery A and Mystery B. Record the results here : Critical angle for Mystery A = 40.4 ° Critical angle for Mystery B = 24.4 ° Step 6 Put the critical angle results into the table below and complete the other columns using the instructions below the table. Material critical angle, C / degrees sin ( C ) 1/sin( C ) refractive index, n Water 49 0.755 1.33 1.33 Glass 42 0.67 1.49 1.49 40.4 0.65 1.54 1.54 ? Mystery B 24.4 2.42 2.421 JDC – Created 05/02/2019 – Printed 20/02/2024 1. Get this number from your work earlier on this page 3. Now press the x –1 button. 4. Get this number from the PhET sim (see example below) 2. On a calculator press the sin button, then type the critical angle, then press the = button. Step 7 Look at the last two columns of the table and use what you see to suggest n for Mystery A and B. refractive index for Mystery A = ……………………………………… ; refractive index for Mystery B = ………………………………………

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Activity 4: Intensity of Reflected ray Step 1 Set the PhET sim up so that it looks like the screenshot below. The material in the top half should be water , the material in the bottom half should be air , and the angle of incidence should be 10°. Catch the reflected ray with the intensity meter as shown in the screenshot. Step 2 Increase the angle of incidence by 10°, catch the reflected beam with the intensity meter to find out what % intensity the reflected beam has. Record your result in the table on the right. Step 3 Complete the rest of the table by making measurements from the sim. Step 4 When the angle of incidence is greater than the critical angle, 100% of the light intensity is reflected. This is called total internal reflection because all the light is reflected. Use the data in the table to suggest a value for the critical angle in water, and explain why you have chosen that angle. 50 degrees because the ray intensity is closer to 0% than 100% Activity 5: Dispersion in Prism The PhET sim also has two other options: Prisms and More Tools . JDC – Created 05/02/2019 – Printed 20/02/2024 angle of incidence / degrees intensity of reflected ray / % 10 2.19 20 2.78 30 4.55 35 6.08 40 9.73 45 18.69 50 100 55 100 60 100 70 100 80 100

Play with these and record the best things you find out in the boxes below. JDC – Created 05/02/2019 – Printed 20/02/2024 As per more tools, the light either bounces or it also goes through whichever refractions. Whenever closer to air it could either go thinner or more high whether closer to glass it can get thicker and more into it. With the prisms you can see how the light shades go trough each shape.

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