Transcript File
Optics Lesson # 4 Reflection in Plane Mirrors Terminology • A plane mirror can be used to show the predictable path of light when it hits the mirror. • The original incoming ray is called the incident ray. • The ray that bounces off the mirror is called the reflected ray. • The normal is the line that is perpendicular (at a right angle) to the reflecting mirror surface. • The normal is drawn at the point where the incident ray strikes the surface of the mirror. • The angle of incidence is the angle between the incident ray and the normal. • The angle of reflection is the angle between the reflected ray and the normal. Laws of Reflection • The angle of incidence equals the angle of reflection in a plane mirror. • The incident ray, the reflected ray, and the normal all lie in the same plane in a plane mirror. Images in Plane Mirrors • A light source radiates millions of light rays in all directions, but you are only concerned with the rays that actually strike the mirror and are reflected into your eyes, with the angle of incidence being equal to the angle of reflection. • In an image, the distance from the object to the mirror is exactly the same as the distance from the image to the mirror and the object is perpendicular to the mirror surface. . • Images are also flipped horizontally and appear in reverse order when looking the mirror. This property is called lateral inversion. SALT • When you describe the properties of an image, you need to examine four characteristics. Use the acronym SALT to help you remember them! • Size of the image (compared to the object – same size, smaller, or larger) • Attitude of the image (which way the image is oriented compared to the object – upright or inverted) • Location of the image (distance from the mirror and object) • Type of image (real or virtual). A real image is formed when light rays converge after striking the mirror, and a virtual image is formed when they diverge or stay parallel. Since light rays stay parallel in a plane mirror, they are considered virtual. SALT in Plane Mirrors • An image in a plane mirror is: – always the same SIZE as the object – its ATTITUDE is upright but laterally inverted – its LOCATION is behind the mirror with the same distance behind the object as in front – its TYPE is virtual. Stealth Technology • Radar (Radio Detection and Ranging) was invented in 1935 and was used to detect aircraft from the ground during WWII. • The stealth fighter was made to avoid detection. • Its first feature is that the paint used on the aircraft absorbs much of the energy from the radar waves. The base of the paint allows the radar waves to penetrate the surface, and then the radar waves reflect from one particle to the next, losing energy along the way. This means the rays are not very strong around the stealth to detect it, but some waves are still reflected. • The second feature that prevents detection is the shape of the airplane. All the surfaces are flat and all the edges are sharp, which means that most of the incoming radar rays will not hit perpendicular to those surfaces, meaning they will not reflect back to the radar antenna. Videos • Reflection – Bill Nye • Stealth Technology Development