Chapter 11 Mirrors and Lenses KEY

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Science 8 Physics Unit http://moodle.sd23.bc.

1 Science 8 Physics Unit Question Completion Asking for Help Working in Class G I have completed all of the assigned questions, completed all diagrams, and corrected all wrong answers. I asked questions during the lesson, or asked for extra help (in or outside of class) when I needed it. I was focussed in class, participated in the lesson and worked hard on my classwork practice. S I completed most of the assigned questions, but did not finish all diagrams required, did not correct wrong answers, or have it done on time. I asked questions or asked for extra help (in or outside of class) when I need it. I was only somewhat focussed in class, participated in the lesson and worked on my classwork practice. N I have not completed the assigned questions or finished the required diagrams. I never got my work done on time. I didn t ask questions in class or ask for extra help when I needed it. I was not focussed in class, didn t participate in the lesson or work very hard on my classwork practice in class. Chapter 11 Mirrors and Lenses KEY Name: Date: Block: Section 11.1 Reflecting Light Off a Plane Mirror (page 313) 1. Define plane mirror: A regular, flat mirror that produces an image by specular reflection. 2. Draw a light ray diagram for a ray that is reflected by a plane (flat) mirror. Label each of the following parts of the diagram: Incident Ray, Reflected Ray, Angle of Incidence, Angle of Reflection, Normal, Point of Incidence 1

2 3. All mirrors reflect light. 4. In a plane mirror, what is the size, attitude, and location of the image in relation to the object? Image is same size, the image is upright (attitude), and the image if found behind the mirror (same distance from mirror as object). Section 11.2 Reflecting Light Off Surfaces (pages ) 1. Define specular reflection: A reflection of light off a smooth, shiny surface. You will be able to see an image. (Mirrors, shiny metal, surface of still lake) 2. State the two laws of reflection. The angle of incidence equals the angle of reflection The incident ray, normal, and reflected ray all lie in the same plane. 3. Define diffuse reflection: When light hits an irregular surface and light is scattered in many directions. No image is formed. 4. What is the largest possible angle of incidence for a light ray traveling toward a mirror? What is the smallest possible angle of incidence? Largest possible angle of incidence for light to travel towards a mirror is 90 degrees. The smallest possible angle of incidence is 1 degree. 5. If the only source of light in a room is one light bulb, why can we see everything in the room? Light rays spread out in all directions and can reflect off all surfaces to distribute light. 6. Give examples of how an interior designer might benefit from knowledge of diffuse reflection. Choose an example of direct light and an example of indirect light in your home. Briefly summarize their effectiveness. Answers may vary Section 11.3 Describing Images (pages ) 1. Describe image: An optical reproduction of an object formed by a lens or mirror. 2. Describe real image: An image that can be placed on a screen 3. Describe virtual image: An image that can not be placed on a screen and can only be seen by looking at or through an optical device. 4. What is an optical device? Give some examples. An optical device is a device that produces an image of an object. Examples camera, LCD, overhead, 2

3 magnifying glass, glasses, our eyes, telescopes, microscopes, movie projectors. 5. List the Characteristics of Images (refer to Table 1 on page 320). a. Size Smaller than the object viewed Larger than the object viewed Same size as the object viewed b. Attitude Upright (right-side up) Inverted (upside down) c. Location On the same side of the lens opposite the object, closer to the optical device than to the object, etc. d. Type Real image (place on a screen) Virtual image (only seen looking at or through an optical device) 6. What does the word upright mean? Inverted? Upright right-side up; Inverted upside down Section 11.6 Using Curved Mirrors (pages ) 1. A concave mirror is a mirror that curves inwards. The image formed by this mirror depends on how far away the object is from the focal point. 2. How can you describe light rays that come together at a focal point? Converging 3. If an object is far from a concave mirror, the image is small and inverted (upside down). This image is considered to be what type of image, virtual or real? Real 4. If an object is close to a concave mirror, then the image appears to be larger than the object and is upright (right-side up). This image is considered to be what type of image, virtual or real? Virtual 5. Give some examples of uses for concave mirrors. Telescopes, cosmetic mirror 6. There are other kinds of radiation energy that we can t see that exist. Explain the shape of satellite dishes that receive radio signals from satellites in orbit around the Earth. A concave shape to focus the weak incoming radio signals to be picked up. 3

4 7. What type of image would you expect to see if you looked at yourself in the bowl of a spoon? A virtual image that is upright if close, a real image that is inverted if far. 8. A convex mirror is a mirror that curves outwards. It reflects parallel light rays as if they came from the focal point behind the mirror. 9. The image of an object in a convex mirror will always be upright and farther (or smaller) from the mirror than the object. This image is considered to be what type of image, virtual or real? Virtual 10. When light rays spread apart after being reflected, they are considered to be what? Diverging 11. What are some examples in life that use convex mirrors? Security mirrors, side mirrors in buses 12. Why are large convex mirrors used for security in stores? (Hint what happens to the light reflecting off of a shoplifter if the storekeeper can see the thief?) A convex mirror will give a large field of view than a plane mirror; therefore, a storekeeper will be able to see more of his/her store with the mirror. 13. Briefly describe how the principal focus in a concave mirror is the same and how it is different from the principal focus in a convex mirror. They are similar because in both cases, the principal focus is the point at which incident parallel light rays are reflected through (concave mirror) or appear to be reflected from (convex mirror). They differ, because the principal focus of a concave mirror is in front of the mirror, whereas the principal focus of a convex mirror is behind the mirror. 14. For each situation, state whether the image produced is real or virtual. Explain how you know. a. A girl is standing close to a cosmetic mirror while applying lipstick. The image is virtual because it is upright and behind the mirror. b. An astronomer is looking at an image of the Moon through her telescope, which has a concave mirror. The image is real, because it is in front of the mirror and could be placed on a screen. c. A clerk in a drugstore is looking at the image of a customer in a surveillance mirror. It is virtual because it is upright and behind the mirror. 15. Which of the following mirrors can produce an upright image: plane mirror, convex mirror, concave mirror? All three can produce an upright image. The concave mirror is the only one to produce an inverted image. This occurs when the object is beyond the principal focus. 4

5 Section 11.7 The Refraction of Light (pages 329) 1. Define refraction: The bending of light as it travels from one material into another. 2. Define angle of refraction: The angle between the refracted ray and the normal. 3. Define refracted ray: A ray of light that has changed direction as it passes through a transparent substance. Section 11.8 Refracting Light in Lenses (pages ) 1. Define lens: A curved, transparent device that causes light to refract as it passes through; gathers light from an object and produces an image of the object. 2. Explain why light bends as it travels from air into water. Light will travel at a different speed in air than in water. Water will then bend the light because light will be traveling slower within the water. 3. Describe what a convex lens looks like. A convex lens is thicker in the middle than at the outside edges. 4. Describe what a concave lens looks like. A concave lens is thinner in the middle than at the outside edges. 5. Does a light ray that passes through the middle of either or convex or concave lens refract light? Why or why not? No, a light ray that passes through the middle of a convex or concave lens will not refract light. At the middle, the light hits the lens at 90 degrees and the light will not bend. 6. What happens to the light rays that pass through a convex lens? Rays converge 7. What happens to the light rays that pass through a concave lens? Rays diverge 8. What is another word or words for normal in relation to light rays? Principal axis 9. A concave lens refracts light rays towards or away from the normal? Away 10. A convex lens refracts light rays towards or away from the normal? Towards the normal (or principal axis) 5

6 11. Make a list of devices that use a least one lens. Cameras, LCD projectors, glasses, magnifying glass, microscope Review of Concepts Mirrors Concave Convex Insert a picture of each mirror here Do the light rays Converge Diverge converge or diverge? Is the image upright *If object farther than focal or inverted? point, than object is inverted *If object closer than focal point, than the object is upright Is the image smaller *Farther than FP Smaller or larger than the *Closer to FP Larger object? *Closer than FP - Larger Upright image Smaller then object Is the image real *Farther than FP Real Virtual or virtual? *Closer to FP - Real *Closer than FP - Virtual 6

7 Lenses Concave Convex Insert a picture of each lens here Do the light rays Diverge Converge converge or diverge? Is the image upright Upright or inverted? *Farther than FP - Inverted *Closer to FP - Upright Is the image smaller Smaller or larger than the object? *>2FP - Smaller *2FP 1FP - Larger *<1FP - Larger Is the image real Virtual *>2FP - Real or virtual? *2FP 1FP - Real *<1FP - Virtual 7

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normal: a line drawn perpendicular (90 ) from the point of incidence of the reflecting surface

normal: a line drawn perpendicular (90 ) from the point of incidence of the reflecting surface Ch 11 Reflecting Light off a Plane Mirror p. 313 Types of Mirrors (3) 1) Plane: flat fg 1 p. 313 law of reflection: the angle of incidence = the angle of reflection incident ray (in): the ray (light beam)