Light Big Idea: Electromagnetic Radiation, which includes light, is a form of radiant energy possessing properties of both waves and zero-mass particles called photons. Photons vary in their energy, which causes them to vary in their frequencies and wavelengths as well. EM radiation can be bent (refracted) or reflected by certain materials, allowing us to manipulate how it travels and what kinds of images it produces. Topic 7.1: Light basics and the EM spectrum Topic 7.2: Refraction Topic 7.3: Reflection and Polarization Topic 7.4: Diffraction and Wave-Particle Duality

I can determine the magnification of a curved mirror. Learning Goal: You will be able to describe the wave-particle view of light and how diffraction occurs. Success Criteria: You will know you have met the learning goal when you can truthfully say: I can describe what will happen when light is reflected off of mirrors of various shapes. I can determine the magnification of a curved mirror. I can describe how light is polarized and how to control its polarization. Image(s) from Bing Images

Success Criteria 1: I can describe what will happen when light is reflected off of mirrors of various shapes. When light strikes an object, the atoms on its surface absorb the photons. It then retains the energy as heat or the electrons in the atom re-emit photons in all different directions. When a material is polished enough, and re-emits enough of the photons that reach it (rather than retaining them as heat), the material appears shiny. If the polished area is large enough, an image can be formed. We call objects that can produce images by reflecting photons in this way mirrors. Image(s) from Bing Images

Success Criteria 1: I can describe what will happen when light is reflected off of mirrors of various shapes. A reflection, thus, is not light “bouncing” off a mirror (from the particle perspective). Photons can’t bounce, they can only be absorbed and re-emitted. Also, an atom doesn’t know to re-emit photons in any given direction. The image that forms comes from the fact that only at a certain angle called the angle of incidence does enough constructive interference of light occur for the image to be created. This angle is the same as the angle of reflection, as you can see in the picture on the left below. Image(s) from Bing Images

Task 7.3.1 (4 points): Answer these questions: Success Criteria 1: I can describe what will happen when light is reflected off of mirrors of various shapes. Task 7.3.1 (4 points): Answer these questions: What are the two things that can happen when a photon hits an atom? What qualities does a material have to have in order to be a mirror? Why is it incorrect to say that light “bounces” off a mirror? If light strikes a mirror at 25° left of the normal (25 ° from perpendicular to the surface) at what angle will the light be reflected? Image(s) from Bing Images

Success Criteria 1: I can describe what will happen when light is reflected off of mirrors of various shapes. When a mirror is curved, the reflected photons (sometimes called rays) change directions. This is because at different points on the mirror, the line perpendicular to the mirror changes. In mirrors that are spherical in their curvature (the curve could be extended to produce a sphere), which are the only kind of curved mirrors that we will consider in this course, relationships can be seen between the distance an object is from the mirror and the distance the object appears from the mirror. This relationship is given with the following equation: 1/p + 1/q = 1/f = 1/(.5C) p = object’s distance from mirror (m) q = image’s distance from mirror (m). In this case, the “image distance” is not how far away it appears to our eyes, but the point where the incident and reflected light rays intersect. f = focal length (the distance to the focal point; the point where parallel light rays will converge) (m) C = radius of curvature (the distance to C, which is the center of the mirror if it were a complete circle) (m). Image(s) from Bing Images

Success Criteria 1: I can describe what will happen when light is reflected off of mirrors of various shapes. When a mirror is concave, the focal point is in front of of the mirror (f and C are positive since they are on the same side of the mirror as the object). When the mirror is convex, the focal point is behind the mirror (f and C are negative since they are on the opposite side of the mirror as the object). In convex mirrors, the image is considered to be “virtual” since light rays don’t actually converge on any point. We can draw how light is reflected off of mirrors to determine the image distance using ray diagrams with rays travelling through the focal point). 1/p + 1/q = 1/f = 1/(.5C) p = object’s distance from mirror (m) q = image’s distance from mirror (m) f = focal length (the distance to the focal point; the point where parallel light rays will converge) (m) C = radius of curvature (the distance to C, which is the center of the mirror if it were a complete circle) (m) Image(s) from Bing Images

Task 7.3.2 (4 points) Answer these questions: Success Criteria 1: I can describe what will happen when light is reflected off of mirrors of various shapes. Task 7.3.2 (4 points) Answer these questions: How far from a concave mirror would a toy car placed 1.5 m from the mirror appear if the mirror had a radius of curvature of 2.2 m? The focal length of a convex mirror is -0.85 m. How far from the mirror is a person if they appear to be 3.5 m away? What is the focal length of a mirror if an object placed 4.0 m away appears to be 5.6 m away? Is the mirror in part c) concave or convex? Image(s) from Bing Images

Task 7.3.3 (6 points) Draw ray diagrams for the following. Success Criteria 1: I can describe what will happen when light is reflected off of mirrors of various shapes. Task 7.3.3 (6 points) Draw ray diagrams for the following. A concave mirror with an object further away than C. A concave mirror with an object at C. A concave mirror with an object between C and F. Image(s) from Bing Images

Success Criteria 2: I can determine the magnification of a curved mirror. When a curved mirror reflects light, the image changes size. This magnification is expressed as a ratio of the object height to the image height, and is given by the equation: M = h’/h = -q/p M = magnification (no units) h‘ = image height (m) h = object height (m) p = object distance (m) q = image distance (m) A magnification of 1 means no magnification. Convex mirrors always have a magnification of less than one, thus they make images appear smaller. Note that if the height of an image is negative, it means the image is inverted. Image(s) from Bing Images

Success Criteria 2: I can determine the magnification of a curved mirror. The effect of having a large objective mirror is that it collects more light and can thus provide more resolution. Magnifying something does no good if it just makes the object appear bigger. It has to add resolution as well. For example, the image on the left has both high magnification and high resolution. The image on the right only has high magnification. Image(s) from Bing Images

Task 7.3.4 (6 points): Answer these questions. Success Criteria 2: I can determine the magnification of a curved mirror. Task 7.3.4 (6 points): Answer these questions. What would be the magnification of a 2.5 cm ball if it appeared to be 3.8 cm? If a microscope makes 0.25 mm tall objects appear to be 1.4 cm tall, what is the magnification? How tall would an object be if it appeared to be 0.27 m with a magnification of 14.5? What is the image height of a book if when placed 2.8 m from a mirror, its image is 2.5 m behind the mirror and its actual height is 18 cm? Look online to find the magnifications of these instruments (2 points): A magnifying glass A common light microscope An electron microscope A common optical telescope The Hubble telescope Image(s) from Bing Images

Success Criteria 3: I can describe how light is polarized and how to control its polarization. As a transverse wave, the amplitude of a light wave is perpendicular to the direction of light propagation. It thus has a direction as well (up and down, left and right, or something in between.). Most light propagates with some waves in all different directions. We call this unpolarized light. Image(s) from Bing Images

Success Criteria 3: I can describe how light is polarized and how to control its polarization. When light interacts with certain types of molecules and in certain ways, it becomes polarized, meaning light that is propagating on a certain plane is transmitted, while other light is absorbed. Image(s) from Bing Images

Answer these questions: How do polarizing filters work? Success Criteria 3: I can describe how light is polarized and how to control its polarization. Task 7.3.5 (4 points): Read the article at http://www.physicsclassroom.com/class/light/Lesson-1/Polarization Answer these questions: How do polarizing filters work? Why does light become polarized when it is reflected off certain surfaces, such as water? Draw a picture of how you could hold two polarizing filters to block all light passing through them. Why do two different images appear through the sample of Iceland Spar? Image(s) from Bing Images

Task 7.3.6 (4 points): Write at least 8 things you learned in this topic (1/2 point each). If you do this in your notebook, please do it in list form rather than paragraph form. Image(s) from Bing Images