Chapter 29 - Reflection 4-15-13 On a separate sheet of paper, write the following Warm-Up Questions and answers: 1. Explain what a virtual image is and give examples (pg. 445). 2. When you view your image in a plane mirror, how far behind the mirror is your image compared with your distance in front of the mirror (see pg. 444)? Be sure to draw diagrams to help explain. Today's Warm-Up questions should be on the same sheet of separate paper that will be turned in before the end of class.

Virtual images as they appear in a mirror. The image appears as far "behind" the mirror as the object is in front of the mirror. The image is formed by the mirror itself.

Why will a camera with automatic focus give poor results if you take a picture of yourself in a mirror? The sonar or infrared beam will reflect from the surface of the mirror and so the camera will focus on the mirror surface instead of the virtual image in the mirror. Since your image in the mirror is farther away than the mirror, the photograph will show a poorly focused image. If you manually focus the camera, then you the image could be clearer and in focus.

Notes: Reflection & Refraction When waves interact with matter (incident upon), they can be reflected, absorbed, transmitted, or a combination of all options. All waves that are transmitted (passing through different material) can be refracted. Reflection When a wave reaches a boundary between two media, usually some or all of the wave bounces back into the first medium.

At an atomic level, waves frequencies are absorbed and then re-emitted. Waves follow the laws of conservation of momentum and energy. As you think of waves reflecting, imagine a billiard game as the cue ball reflects off of objects and the bumpers within the table. In each case, the angle of incidence will equal the angle of reflection.

Label the example below by indicating points of light reflection, transmission, and refraction.

Metals reflect almost all frequencies of visible light. If you shine a light directly on the surface of still water or glass (straight into the surface; at an angle close to 90), only a very small percentage (4%) of its energy is reflected; the rest is transmitted. If the back side of the glass is darkened, reflection is more noticeable. Mirrors produce virtual images, meaning they are images that appear in a location where light does not really reach.

Virtual Image vs. Real Image

Mirage Maker

Interesting thought: Because of the finite speed of light, your image in the mirror is always younger than you.

Diffuse reflection - when light is incident upon a rough surface, it is reflected in many different directions (the most common type of reflection). Compare a highly waxed floor to an unpolished floor. The opposite of diffuse reflection is Specular Reflection (mirror-like reflection). Sound Reflection (acoustics) - sound energy can also reflected, absorbed, or transmitted. An echo is a single reflection of a sound wave; reverberations are multiple reflections of sound waves.

Acoustically-designed diffuse reflection

Practice your ray diagrams; Today's assignment: Submit today's Warm-Up Questions with the notes and diagrams for credit. New Assignment (worksheet): Practice Page: Reflection & Refraction (Ch. 29) Practice your ray diagrams; USE A STRAIGHT-EDGE! Tomorrow - Lab Activity: Lenses (begin Ch. 30)