Physics Themed 1516 Williams. Mirrors & Reflective Optics

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1 Physics Themed 1516 Williams Mirrors & Reflective Optics 1

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3 Flat Ray Tracing Exercise The black dot represents where an image from the "tip of the flickering flame" would appear to be to any observer behind the mirror. The fact that a single point from an object maps out to a single point for an image is the reason that mirrors form images. If the rays you traced did not converge to a single point, the image would be blurred. Below, draw four light rays carefully. Draw an eyeball to show where the viewer believes light is traveling in a straight line to them. Label: 1. The mirror 2. The object (tip of the flickering flame) 3. The image (tip of the flickering flame) 4. A normal (there are 19 possible ones pre-drawn for you!) 5. One instance of law of reflection (angle of incidence = angle of reflection) We will use an arrow to represent a candle with the point being the tip of the flickering flame. Repeat the previous process for at least two light rays. This process is called "ray tracing". Approximate angles. 3

4 Mirror, light and color lab Station 1: Concave mirror Resources: Several numbered concave mirrors, white paper Activity: Find: focal length for several small mirrors by projecting distant light onto a white surface. Predict where "no image" should be seen while looking in mirror. Questions: 1. Record the focal length for each mirror below: 2. Based on focal length value, a. Predict for each mirror, at what distance from your face should no image form when you look into the mirror. b. Test each. i. What did you see? ii. Do images clearly form at both closer and farther object distances? c. At what distance should your magnification be 1 for each mirror? (Try it) d. What happens to magnification when you hold the mirror closer? farther? 3. Why do you project an object using distant light? Station 2: Flash light Resources: Flashlight, white paper, concave, convex and flat mirrors Activity: Shine a flashlight at a wall. Observe and answer the questions below. Questions: 1. Does the light spread out as expected, or does it exit as a narrow beam? 2. What advantage is there to a focused, narrow beam of light over a diffuse light beam spreading light more widely? 3. Does a flashlight contain a mirror? What type? 4. Where is the bulb relative to the mirror (use precise mirror vocabulary here) 5. What is special about placing a bulb in the location if the goal is to make a narrow beam of light? 6. Car lights ALL have the same kind of bulb and mirror geometry. Why is this useful for a car too? 7. Aim the flashlight at each mirror type. Which mirror converges the light beam? 8. Where is the bulb relative to the mirror (use precise mirror vocabulary here) 9. To get the light beam to converge to a single point at the focal point, should the flashlight be placed at the focal point of the concave mirror. At a very distant point? Why or why not? 10. Car lights ALL have the same kind of bulb and mirror geometry. Why is this useful for a car too? 4

5 Station 3: Field of view test Resources: Three small mirrors: Convex, Concave and Flat. Partner. Activity: Look at flat, concave and convex mirrors at partner walking from behind on either your left of right side. See where "blind spot" forms. compare this to road and usefulness in cars, where does person disappear) Questions: 1. Rank in order which mirrors provide the best field of view (biggest viewing angle) 2. Which mirror makes object appear smaller, but doesn't turn them upside down? 3. Which mirror would be useful as a side view mirror for a car? Why? 4. Which mirror would be best at "seeing around corners"? 5

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7 Computer lab day activity 7

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10 Note which mirrors always make which kind of images!...this is asked on the quest in multiple ways! 10

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15 Unit 3 Vocabulary and Equations Mirrors & Reflection Symbols: R, G, B, C, Y, M, f, T, v, λ Equations & Constants f = 1/T, v = f λ wave speed = v, Period = T, Frequency = f, V light = c = 3 x 10 8 m/s, v sound ~ 340 m/s v sound = T( C); Lens/mirror: 1/d o + 1/d i = 1/f Magnification: M = -d i / d o M = h i / h o A 0 = 27.5 Hz 2 (1/12) = I Δ inversely with r 2 Wave length = λ d = v t Beats = f 1 - f 2 M = V 0 /v sound Δ: +10 db = 2x Vol = 10x I Life Skills & Traditional Objectives - Williams 1. The student understands all vocabulary, math, demos, videos, class assignments and discussions 2. The student remembers objectives & vocabulary from previous units. 3. The student understands specular and diffuse reflection including reflection off paper vs. mirrors 4. The students knows how the brain locates objects in space and why we see images as illusion of objects 5. The student can ray trace and distinguishes between incident and reflected light rays in image formation 6. The student can draw and identify a normal and understands the law of reflection 7. The student knows the light rays an observer sees and doesn't see when looking at images in a mirror 8. The student can apply and make sense of the three principal rays using mirror geometry and logic 9. The student can find the two easiest principal ray for convex and concave mirrors 10. The student understands all reflected light rays from any object point will converge post-reflection at some location in space to form an image (or no image is seen) 11. The student understands how "horizontal" light rays emerge from distant sources and diverging light rays emerge from source close to the mirror 12. LS: The student can recite the three mirror types used in car and why their special properties make them ideally suited for the very different jobs they do 13. The student knows other mirror uses besides in cars 14. LS: The student knows how satellite dishes work and why are truly mirrors - just not visible light mirrors 15. The student has created a 3 x 5" information sheet on an index card including information on how images change with object location DuPage ROE Objectives 801. I can distinguish between transverse or longitudinal waves I can identify waves as either mechanical or electromagnetic I can identify: wavelength, amplitude, crest, trough, and period, given a visual representation. Numbered Unit Vocabulary list (you need to know all previous vocabulary too) 1. diffuse 2. specular 3. Matte 4. Object 5. Image 6. ray tracing 7. diverge 8. converge 9. normal 10. perpendicular 11. flat 12. planar 13. plane 14. angle of incidence 15. angle of reflection 16. focal point 17. focal ray 18. horizontal ray 19. center ray 20. center point 21. curved mirror 22. convex 23. concave 24. principal axis 25. principal ray 26. image properties 27. upright 28. inverted 29. enlarged 30. reduced 31. real 32. virtual 33. blind spot 15

16 Mirrors & Reflection Calendar: (Williams) Bold and underlined means put in journal notes; theme of day at start in bold Mod Date Plans Homework (04-01) and (04-02) Large mirrors?, String demo, candle demo, need rulers 1st period, 2nd period: Ray Tracing mechanics & 3 principal rays (can't be here tomorrow, 8:15 meeting) 1 Fr:09/18/15 Start HW H Mo:09/21/15 Assembly 3 Tu:09/22/15 4 We:09/23/15 5* Th:09/24/15 6-Home Coming Fr:09/25/15 Assembly Meeting Periods 1 & 2, provide packet ray tracing solutions (04-03) Ray tracing H04-02 Finish up any notes as necessary Mirror mini-lab Group work time/group Quiz H04-03 (04-04) Last mirror notes Preview computer simulation, see what room you're in tomorrow H04-04 Computer lab day: Answer property trends questions, make "cheat sheet", do HW H04-05 Any questions/catch up on anything, demo lab sim Color vision video Homecoming Go over computer lab results and questions Review for test/finish anything Study for test 7 Mo:09/28/15 8 Tu:09/29/15 Mirrors/reflection test (~ 70 pts) None 16