Week 5 Lab Reflection 2017_1

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Feb 20, 2024

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Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022 INTRODUCTION REFLECTION OF LIGHT Reflection of light (and other forms of electromagnetic radiation) occurs when the waves encounter a surface or other boundary that does not absorb the energy of the radiation and bounces the waves away from the surface. The simplest example of visible light reflection is the surface of a smooth pool of water, where incident light is reflected in an orderly manner to produce a clear image of the scenery surrounding the pool. Throw a rock into the pool (see Figure 1), and the water is perturbed to form waves, which disrupt the reflection by scattering the reflected light rays in all directions. Some of the earliest accounts of light reflection originate from the ancient Greek mathematician Euclid, who conducted a series of experiments around 300 BC, and appears to have had a good understanding of how light is reflected. However, it wasn't until a millennium and a half later that the Arab scientist Alhazen proposed a law describing exactly what happens to a light ray when it strikes a smooth surface and then bounces off into space. The incoming light wave is referred to as an incident wave, and the wave that is bounced away from the surface is termed the reflected wave. Visible white light that is directed onto the surface of a mirror at an angle (incident) is reflected back into space by the mirror surface at another angle (reflected) that is equal to the incident angle, as presented for the action of a beam of light from a flashlight on a smooth, flat mirror in Figure 2. Thus, the angle of incidence is equal to the angle of reflection for visible light as well as for all other wavelengths of the electromagnetic radiation spectrum. This concept is often termed the Law of Reflection . It is important to note that the light is not separated into its component colors because it is not being "bent" or refracted , and all wavelengths are being reflected at equal angles. The best surfaces for reflecting light are very smooth, such as a glass mirror or polished metal, although almost all surfaces will reflect light to some degree.

Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022 Because light behaves in some ways as a wave and in other ways as if it were composed of particles, several independent theories of light reflection have emerged. According to wave-based theories, the light waves spread out from the source in all directions, and upon striking a mirror, are reflected at an angle determined by the angle at which the light arrives. The reflection process inverts each wave back-to-front, which is why a reverse image is observed. The shape of light waves depends upon the size of the light source and how far the waves have traveled to reach the mirror. Wavefronts that originate from a source near the mirror will be highly curved, while those emitted by distant light sources will be almost linear, a factor that will affect the angle of reflection. According to particle theory, which differs in some important details from the wave concept, light arrives at the mirror in the form of a stream of tiny particles, termed photons, which bounce away from the surface upon impact. Because the particles are so small, they travel very close together (virtually side by side) and bounce from different points, so their order is reversed by the reflection process, producing a mirror image. Regardless of whether light is acting as particles or waves, however, the result of reflection is the same. The reflected light produces a mirror image. To visualize the differences between specular and diffuse reflection, consider two very different surfaces: a smooth mirror and a rough reddish surface. The mirror reflects all of the components of white light (such as red, green, and blue wavelengths) almost equally and the reflected specular light follows a trajectory having the same angle from the normal as the incident light. The rough reddish surface, however, does not reflect all wavelengths because it absorbs most of the blue and green components, and reflects the red light. Also, the diffuse light that is reflected from the rough surface is scattered in all directions.

Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022 Perhaps the best example of specular reflection, which we encounter on a daily basis, is the mirror image produced by a household mirror that people might use many times a day to view their appearance. The mirror's smooth reflective glass surface renders a virtual image of the observer from the light that is reflected directly back into the eyes. This image is referred to as "virtual" because it does not actually exist (no light is produced) and appears to be behind the plane of the mirror due to an assumption that the brain naturally makes. The way in which this occurs is easiest to visualize when looking at the reflection of an object placed on one side of the observer, so that the light from the object strikes the mirror at an angle and is reflected at an equal angle to the viewer's eyes. As the eyes receive the reflected rays, the brain assumes that the light rays have reached the eyes in a direct straight path. Tracing the rays backward toward the mirror, the brain perceives an image that is positioned behind the mirror. An interesting feature of this reflection artifact is that the image of an object being observed appears to be the same distance behind the plane of the mirror as the actual object is in front of the mirror. PRE-LAB QUESTIONS 1. What is the Law of Reflection? The law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection. 2. What is an incident wave? An incident wave is a wave that is approaching a boundary and when it hits the wave becomes a reflected wave. 3. What is a reflected wave? A reflected wave is one that involves a change in direction of waves when they bounce off a barrier. 4. What is specular reflection? A specular reflection is defined as light reflected from a smooth surface at a definite angle. 5. What is diffuse reflection? A diffuse reflection is defined as light reflected in all directions from a rough surface. 6. Does a mirror produce specular or diffuse reflection? A mirror produces a specular reflection. 7. What is a virtual image? A virtual image is an image, such as one seen in a plane mirror, formed of points from which divergent rays seem to emanate without actually doing so.

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Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022 MATERIALS 1. A flat mirror (if it’s a loose mirror, you’ll also need something to make it stand up). Note a bathroom mirror can be used, you’ll just need something to raise up your paper to the height of the mirror. 2. Paper 3. Pen or pencil 4. cm ruler 5. protractor (or cut out protractor from page below) 6. straight pin (or something like it) 7. Camera (or scanner) OBJECTIVE To determine how rays of light reflect off the surface of mirrors. QUESTION How do the angle of incident light rays compare to the angle of reflected light rays? HYPOTHESIS My hypothesis is that the angle of incident light rays will be the same as the angle of reflected light rays because of the law of reflection. EXPERIMENT 1. Take a sheet of any white 8.5”x11 paper – fold it in half then with a ruler, draw a line across the paper on the fold to divide the paper into two equal halves.

Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022 2. Stand your mirror on the line. Place the silver backing edge of your flat mirror on the line you have drawn. Make sure the mirror stands straight and does not move by using clips as shown (you can also tape or rubber band the mirror to a block, or use clothes pens – whatever is at hand and holds the mirror steady). It is important that the mirror does not move or change position during this activity . Note: If you are using a bathroom mirror you will fold your paper in half down the line you drew and place the line against the mirror. You will want to make sure your paper does not move at all during the activity. 3. Draw an “+” on the paper in front of the mirror (slightly to one side). It helps to put extra marks on the “+” to help identify front/back and left/right while looking at the reflection. Stick a straight pin or needle in the center of the “+” to help line up the reflection in the mirror.

Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022 4. Get your eye down to the level of the paper on the table and look at the reflection of the +/pin in the mirror. From the position where your eye sees the reflected image in the mirror – take a ruler and draw a line to where the +/pin appears to be in the mirror. Line the ruler up as if you were making a billiards shot - be careful - draw the line exactly toward the mirror where the image seems to appear. (Label this Line 1) 5. Draw another line as above – viewing the object in the mirror from a slightly different angle with your eye. (Label this Line 2)

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Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022 6. You should now have two lines drawn from the two positions where your eye viewed the object toward the mirror. These lines represent the rays of light that are reflected from the object – off the mirror – to your eyes. We will now remove the mirror and finish our light ray diagram. 7. Set the mirror aside (if you are using a bathroom mirror: remove your paper and unfold it) - we now have just the two lines on the paper directed toward the line that divided the paper in half (where the mirror was placed). With a ruler, extend your two lines to the mirror and then continue to extent the lines until the lines meet behind the line of the mirror (as shown here). The lines behind the mirror meet at the position where the

Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022 image appears to be (behind the mirror). Images that appear behind a mirror are known as virtual images . 8. Fold your paper in half along the line where the mirror was placed and look through the paper by holding it up to the light (it should look like the picture here). If the lines behind the mirror go through the “+”object – you have done an excellent job drawing your lines. 9. This diagram was made to explain the picture above. The dashed lines on the left are rays of light coming from the object toward the mirror line at bottom of the picture (where you folded the paper). These rays reflect off the mirror exactly to the positions where your eyes viewed the image in the mirror. Note that the angle that rays come to the mirror (angle of incidence) and the angle that the rays are reflected from the mirror (angle of reflection) appear to be the same angles. 10. On your paper, label the parts from the diagram below: object being viewed, light rays from object to mirror, light rays from mirror to eye, eye positions viewing reflected

Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022 image, angle of incidence and angle of reflection (these angles are not on the diagram below). 11. You will need to photograph or scan this diagram and submit it with this assignment. Please place your photo in the data section below. DATA 1. Please place a picture of your labelled diagram from the lab here.

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Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022 2. Referring back to Step 8 “ Fold your paper in half along the line where the mirror was placed and look through the paper by holding it up to the light (it should look like the picture here). If the lines behind the mirror go through the “+”object – you have done an excellent job drawing your lines.” How did the lines behind the mirror match up to the + object? They matched pretty close to the + object almost spot on. 3. Measure your angle of incidence using a protractor (or use the one from below). Record this value in the data table below. 4. Measure your angle of reflection using a protractor. Record this value in the data table below. Angle of Incidence Angle of Reflection Line 1 10 9 Line 2 11 10 DISCUSSION 1. How did your angle of incidence compare to your angle of reflection? My angle of

Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022 incidence when compared to the angle of reflection is off by 1 degree. 2. How does the Law of Reflection apply to your answer to the question above? The Law of Reflection applies quite accurate to the question stated above. 3. Please summarize what you learned about reflection. Reflections are very interesting, the angles at which light rays bounce from the mirror to your eyes equals the angle of the distance the light rays travel form the mirror to your eyes. This had surprised me that someone had found such a phenomenon. CONCLUSION Was your hypothesis correct? Explain. My hypothesis was wrong although, the angle of incident lights rays would have equaled the angle of reflected light rays but the only the thing I had close to a ruler was a straight edge. To conclude the straight edge was most likely not that straight. Protractor

Week 5 Lab: Light Reflection Jaden Knodel May 8, 2022

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