20200518_PSCI_1422_Lab 4_Reflection_Refraction and Total Internal Reflection_Lab_Pokhrel Handout(2)

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Apr 3, 2024

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Physics LAB 4: Ray Tracing, Laws of refrac6on and Snell’s Law using a Virtual Setup: Virtual Lab Name: Isabelle Rodriguez Introduc6on: 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 reﬂecEon. The light that enters the glass is said to have been “refracted”, or to have undergone refracEon. When we examine the properEes of transparent medium like glass, it is important to first realize that glass work on the principle of reﬂecEon/refracEon and that lenses (and prisms) work on the principle of refracEon. Where mirror works on the principle of reﬂecEon only. Lenses and mirrors are oMen 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 reﬂecEon. Figure: Reﬂec6on and refrac6on of light at the interface of air and glass Ac6vity 1 : Go to this is the link : hPps://phet.colorado.edu/en/simulaEon/bending-light When the site opens, scroll down unEl you see a light blue circle with PHYICS inside. Click this circle. Then select Light & RadiaEon. Next, find the App called “Bending of Light.” Finally, click on the app (you may click on the Play buPon or the Red 5) You will start the lab using the Intro secEon. Preliminary InvesEgaEon [turn over]

1. Turn the laser on by clicking the red buPon. You will see light ge]ng reﬂected and refracted, but you will be focusing only on reﬂected ray for this part of the experiment. Now move the laser pointer leM and right to change the angle of incidence as shown in figure and verify the laws of reﬂecEon. 2. What are some observaEons you make on angle of reﬂecEon when you change the angle of incidence? Describe them, ( answer, explain, evidence). When moving the incidence angle of reﬂecEon is equal to it. So at a incidence angle of 30 degrees the reﬂecEon is also at 30 degrees. 3. What are the laws of reﬂecEons? Do you think, laws of reﬂecEon hold in your experiment? if it holds describe, ( answer, explain, evidence). Yes, they correlate with the laws or reflection because the reflection angle are the same as the incidence angles. As long as they are both equal they hold in the experiment. Ac6vity 2 : Go to this is the link : hPps://phet.colorado.edu/en/simulaEon/bending-light When the site opens, scroll down unEl you see a light blue circle with PHYICS inside. Click this circle. Then select Light & RadiaEon. Next, find the App called “Bending of Light.” Finally, click on the app (you may click on the Play buPon or the Red 5) You will start the lab using the Intro secEon. Preliminary InvesEgaEon 4. Turn the laser on by clicking the red buPon. You will see light ge]ng reﬂected and refracted. Now move the laser pointer leM and right by clicking and holding on the silver part and moving it. What are some observaEons you make? Describe them, ( answer, explain, evidence). Move the laser pointer, leM and right by clicking and holding on the silver part and moving it. 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 observaEons? ( answer, explain, evidence). I have observed that incident ray is equal to the reflected ray. On the other hand the reflected ray is smaller in angle compare to the incident ray and reflected ray. Incident Angle (Degrees)= Reﬂected Angles (Degrees) 15 15 30 30 45 45 60 60 JDC – Created 05/02/2019 – Printed 14/06/2020

6. Put the iniEal material back to Air. Now click on water in the lower material. Change it to several other materials and made record your observaEons. Is there are way to make the light, go straight from AIR into the lower material, ( answer, explain, evidence). No, because the laser beam that travel from air to water tend to bent due to waters higher refraction index. The only way to make the light go straight on the lowers material is to change it into air so that the light can travel with a lower refraction index making it not to refract or bent. PART I 1. For this part of the lab you will stay in the intro secEon. 2. Keep the starEng 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 doPed 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 45 32 60 40 75 46 90 90 JDC – Created 05/02/2019 – Printed 14/06/2020

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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 . n1= 1.00 Therefore, you may use n2= sin 0 1/ sin02 In this equaEon, the following variables are used: n2= the index of refracEon for the medium that contains the angle of refracEon. sin01= the sine of the angle of incidence sin02= the sin of the angle of refracEon 6. If you repeat the same experiment with “Glass” which has a higher index of refracEon than water (air was less than water). How did this change the way the Laser Light bent? 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 RefracEon. Total Internal RefracEon 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 ReﬂecEon. The reﬂecEon you see at the lower angles is just Internal ReﬂecEon. It is not total because some light refracts, and some reﬂects. The iniEal angle where Total Internal ReﬂecEon occurs is called the criEcal angle. For light going from Glass to Water it must be somewhere between 60° and 75°. Ac6vity 3 : InvesEgaEng criEcal angle and Total Internal ReﬂecEon using a PhET simulaEon Step 1 Go to hPps://phet.colorado.edu/en/simulaEon/bending-light , click on the buPon. 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 boPom half should be air , and the angle of incidence should be about 30°. n 1 Sin θ 1 = n 2 Sin θ 2 , You will be solving for θ 2 JDC – Created 05/02/2019 – Printed 14/06/2020

Step 2 Gradually increase the angle of incidence unEl i = 40°. The cropped screenshot on the right should help. Read off and record the angles of reﬂec3on and refrac3on below . Angle of reﬂecEon = … …40… ……… ° Angle of refracEon = …… …55… ……… ° Step 3 Keep increasing the angle of incidence unEl the angle of refracEon 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 “ cri6cal angle ” for water. Record the cri3cal angle for water here : CriEcal angle for water = …… 49…………… ° Step 4 JDC – Created 05/02/2019 – Printed 14/06/2020

Return the angle of incidence to 0° and change the material in the top half to glass. Repeat step 3 to find the criEcal angle for glass. Record it here : CriEcal angle for glass = …… 42… ………… ° Step 5 Repeat the process to find the criEcal angle for material Mystery A and Mystery B. Record the results here : CriEcal angle for Mystery A = …… 40.4 …………… ° CriEcal angle for Mystery B = … …24.4… ………… ° Step 6 Put the criEcal angle results into the table below and complete the other columns using the instrucEons below the table. Material criEcal angle, C / degrees sin ( C ) 1/sin( C ) refracEve index, n Water 49 0.755 1.33 1.33 Glass 43 0.682 1.466 1.00 Mystery A 25 0.422 2.366 1.54 Mystery B 47 0.732 1.37 2.42 JDC – Created 05/02/2019 – Printed 14/06/2020 3. Now press the x –1 buPon. Step 7 Look at the last two columns of the table and use what you see to suggest n for Mystery A and B. 1. Get this number from your work earlier on this refracEve index for Mystery A = ……………………………………… ; refracEve index for Mystery B = ………………………………………

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Ac6vity 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 boPom 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 angle of incidence / degrees intensity of reﬂected ray / % 10 2.19 20 2.84 30 4.60 35 6.08 40 10.70 45 18.69 50 100 55 100 60 100 70 100 80 100 JDC – Created 05/02/2019 – Printed 14/06/2020

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 criEcal angle, 100% of the light intensity is reﬂected. This is called total internal reﬂec6on because all the light is reﬂected. Use the data in the table to suggest a value for the criEcal angle in water, and explain why you have chosen that angle. …………………………………………………….…………………………………………………….………………………………………………………………………. …………………………………………………….…………………………………………………….………………………………………………………………………. Ac6vity 5: Dispersion in Prism The PhET sim also has two other opEons: Prisms and More Tools . Play with these and record the best things you find out in the boxes below. JDC – Created 05/02/2019 – Printed 14/06/2020

20200518_PSCI_1422_Lab 4_Reflection_Refraction and Total Internal Reflection_Lab_Pokhrel Handout(2)

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