CHAPTER 18 REFRACTION & LENSES

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1 Physics Approximate Timeline Students are expected to keep up with class work when absent. CHAPTER 18 REFRACTION & LENSES Day Plans for the day Assignments for the day Refraction of Light o Snell s Law Assignments 18.0 & 18.1 Read section(s) 18.2 o Total Internal Reflection Uses of o Mirages o Rainbows Convex & Concave Lenses o Convex Lenses aka Positive Lens, Converging Lens o Image Formation o Image Characteristics Image distance Image size Image orientation Real vs. Virtual Images Convex & Concave Lenses Assignment 18.2 o Concave Lenses aka Negative Lens, Diverging Lens o Image Formation o Image Characteristics o Defects of Spherical Lenses Chromatic Aberrations 4 Applications of Lenses o Eyes o Microscopes o Telescopes o Binoculars o Cameras 5 Lens lab 6 Work on Lens Lab 7 Review for Chapter 18 Test 8 Chapter 18 Test

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3 Study Guide Chapter 18 Quizzes Quiz 18.1 Refraction of Light 1. Define refraction. 2. Write Snell s law in the form of a mathematical equation. 3. In Snells s law we see the variable n. What does n represent? 4. When light travels from an area with low index of refraction into an area with high index of refraction the light ray is bent the normal. 5. When light travels from an area with high index of refraction into an area with low index of refraction the light ray is bent the normal. 6. Define the term critical angle. 7. Solve problems involving Snell s Law. Quiz 18.2 Convex and Concave Lenses 8. Explain the difference in the shape of a convex lens and a concave lens. 9. Write the thin lens equation. 10. Write the equation used to find the magnification of an image. 11. Under what conditions will a convex lens produce: a. a real image? b. a virtual image? 12. Under what conditions will a concave lens produce: a. a real image? b. a virtual image? 13. Spherical lenses create image defects when light passes through the outer edges of the lens. this defect is called. 14. Solve problems involving curved lenses. Quiz 18.3 Applications of Lenses 15. Consider the human eye. a. What does the primary focusing? b. What fine tunes the focusing?

4 Study Guide Chapter 18 Test At the completion of chapter 18 you should 1. Know the definitions of the following terms. a. Index of Refraction b. Snell s Law of Refraction c. Critical Angle d. Total Internal Reflection e. Dispersion f. Lens g. Convex Lens h. Concave Lens i. Thin Lens Equation j. Chromatic Aberration k. Achromatic Lens 2. Know which direction a ray of light is refracted upon entering a new medium. 3. Know and apply Snell s Law of Refraction. 4. Understand how refraction increases the amount of time we see daylight. 5. Understand total internal reflection and its main application. 6. Understand and explain how mirages are formed. 7. Understand and explain how rainbows are formed. 8. Know the alternate names for convex and concave lenses. 9. Understand how images are formed by convex and concave lenses. 10. Calculate the location and size of images formed by convex and concave lenses. 11. Describe the characteristics of images formed by convex and concave lenses.

5 Assignment 18.0 Vocabulary Define each of the following terms. 1. Index of Refraction 2. Snell s Law of Refraction 3. Critical Angle 4. Total Internal Reflection 5. Dispersion 6. Convex Lens 7. Concave Lens 8. Thin Lens Equation 9. Chromatic Aberration 10. Achromatic Lens

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7 Assignment 18.1 Refraction of Light Short Answer: Answer each question in the space provided. Write or print clearly. IF I CAN T READ IT, IT S WRONG. 1. How does the angle of incidence compare with the angle of refraction when a light ray passes from air into glass at a nonzero angle? 2. How does the angle of incidence compare with the angle of refraction when a light ray leaves the glass and enters air at a nonzero angle? 3. Regarding refraction, what is the critical angle? 4. Which substance, A or B, in the figure to the right has a larger index of refraction? Explain. 5. A light ray strikes a boundary between two transparent media. What is the angle of incidence for which there is no refraction? 6. How does the speed of light change as the index of refractions increases? 7. How does the size of the critical angle change as the index of refraction increases?

8 Problems: Solve each of the following problems. Show all work. Circle your answer expressed with the correct number of significant figures and units. 8. A ray of light travels from air into a liquid, as shown to the right. The ray is incident upon the liquid at an angle of 30.0º. The angle of refraction is 22.0º. A) Using Snell s law, calculate the index of refraction of the liquid. B) Compare the calculated index of refraction to those in Table What might the liquid be? 9. Light travels from flint glass into ethanol. Then angle of refraction in the ethanol is 25.0º. What is the angle of incidence in the glass? 10. A beam of light strikes the flat, glass side of a water filled aquarium at an angle of 40.0º to the normal. For glass, n = 1.50; for water n = 1.33 A) At what angle does the beam enter the glass? B) At what angle does the beam enter the water?

9 11. Refer to Table Use the index of refraction of diamond to calculate the speed of light in diamond. 12. Refer to Table Find the critical angle for a diamond in air. 13. A light source is located 2.0 m below the surface of a swimming pool and 1.5 m from the edge of the pool as shown to the right. The pool is filled to the top with water. A) At what angle does the light reaching the edge of the pool leave the water? B) Does this cause the light viewed from this angle to appear deeper or shallower that it actually is?

10 14. The ray of light shown at the right is incident upon a 60º-60º-60º glass prism, n = 1.5. A) Using Snell s law, determine the angle, 2, to the nearest degree. B) Using elementary geometry, determine the value of 1. C) Determine A ray enters a block of crown glass, as shown below. Use a ray diagram to trace the path of the ray until it leaves the glass.

11 Assignment 18.2 Convex & Concave Lenses Short Answer: Answer each question in the space provided. Write or print clearly. IF I CAN T READ IT, IT S WRONG. 1. How do the shapes of convex and concave lenses differ? 2. Locate and describe the physical properties of the image produced by a convex lens when an object is placed some distance beyond 2F. 3. To project an image from a movie projector onto a screen, the film is placed between F and 2F of a converging lens. This arrangement produces an image that is inverted. Why does the filmed scene appear to be upright when the film is viewed? 4. Describe why precision optical instruments use achromatic lenses. 5. Suppose that the figure below is redrawn with a lens of the same focal length but a larger diameter. A) Explain why the location of the image does not change. B) Would the image be affected in any way?

12 6. A swimmer uses a magnifying glass to observe a small object on the bottom of a swimming pool. She discovers that the magnifying glass does not magnify the object very well. Explain why the magnifying glass is not functioning as it would in air. Problems: Solve each of the following problems. Show all work. Circle your answer expressed with the correct number of significant figures and units. 7. A converging lens has a focal length of 25.5 cm. If it is placed 72.5 cm from an object, at what distance from the lens will the image be located? 8. An object is 10.0 cm away from a converging lens that has a focal length of 5.00 cm. How far from the lens will the image be? 9. A convex lens is needed to produce an image that is 0.75 times the size of the object and located 24 cm from the lens on the other side. What focal length should be specified? 10. A 3.0 cm tall object is placed 22 cm in front of a converging lens. A real image is formed 11 cm from the lens. What is the size of the image?

13 11. A diverging lens has a focal length of 15.0 cm. An object placed near it forms a 2.0 cm high image at a distance of 5.0 cm from the lens. A) What are the object position and object height? B) The diverging lens is now replaced by a converging lens with the same focal length. What are the image position, height, and orientation? C) Is it a virtual image or a real image?

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15 Assignment 18.3 Application of Lenses Short Answer: Answer each question in the space provided. Write or print clearly. IF I CAN T READ IT, IT S WRONG. 1. Describe how the human eye focuses light. 2. What is the condition in which the focal length of the eye is too short to focus light on the retina? 3. When subjected to bright sunlight, the pupils of your eyes are smaller than when they are subjected to dimmer light. Explain why your eyes can focus better in bright light. Problems: Solve each of the following problems. Show all work. Circle your answer expressed with the correct number of significant figures and units. 4. To clearly read a book 25 cm away, a farsighted person needs the image to be 45 cm from her eyes. What focal length is needed for the lenses in her eyeglasses? 5. The convex lens of a copy machine has a focal length of 25.0 cm. A letter to be copied is placed 40.0 cm from the lens. A) How far from the lens is the copy paper? B) How much larger with the copy be?