Optics 1 - Reflection of Light PDF

7.4 Optics 7.4.1 Light Incident on a Boundary and Reflection Chapter 8 Sections 8.1 - 8.14 Processes that can take place when light is incident on a boundary between two media 1. Reflection 2. Refraction (transmission) 3. Absorption Reflection Reflection occurs when light bounces off an objec...

7.4 Optics 7.4.1 Light Incident on a Boundary and Reflection Chapter 8 Sections 8.1 - 8.14 Processes that can take place when light is incident on a boundary between two media 1. Reflection 2. Refraction (transmission) 3. Absorption Reflection Reflection occurs when light bounces off an object. If the surface is smooth like glass, water or polished metal, the light will reflect at the same angle as it hits the surface. Refraction (Transmission) Refraction occurs when light bends from a straight path in passing from one medium (e.g. air) into another (e.g. glass) in which its velocity is different. L. Bonello Page 1 7.4 Optics Absorption Absorption occurs when light is captured by matter (or a medium), converting the energy of photons (energy of light waves) into internal energy. When light is absorbed, heat is generated. L. Bonello Page 2 7.4 Optics Transparent Light passes through transparent materials e.g. air, water and clear glass.. Opaque An opaque object is a material which does not allow light to pass through it. L. Bonello Page 3 7.4 Optics Translucent A translucent material allows some light to pass through. Reflection at Plane Surfaces When light falls on a surface, some of the light is reflected and the rest of the light is absorbed by the material. However, when light falls on a good reflector, such as a mirror, all the light tends to be reflected in such a way that the angle of incidence is equal to the angle of reflection. Figure 1 L. Bonello Page 4 7.4 Optics Where: XY = Plane surface (mirror) AO = incident ray OB = reflected ray ON = normal (the imaginary line that is drawn at right angles to the plane reflecting surface.) Angle i = angle of incidence Angle r = angle of reflection Angle i = Angle r Point O = point of incidence (It is the point where the incident ray, the reflected ray and the normal all meet.) Laws of Reflection 1. The reflected ray is in the same plane as the incident ray and the normal to the reflecting surface, at the point of incidence. 2. The angle of reflection is equal to the angle of incidence. Image in a Plane Mirror See Figure 2 below: The image in a plane mirror is: 1. virtual (not real and cannot be formed on a screen) 2. laterally inverted ( the right arm of a person is seen on the left side and vice versa) 3. same size as the object L. Bonello Page 5 7.4 Optics 4. as far behind the mirror as the object is in front 5. and the line joining the object and image is perpendicular to the mirror i.e. the distance OE = the distance IE. Figure 2 Real and Virtual Images Real Image Virtual Image 1. After reflection or After reflection or refraction, refraction, rays actually meet rays appear to meet at a at a point. point. 2. Can be formed on a Cannot be formed on a screen. screen. 3. Always inverted. Always erect. Table 1 L. Bonello Page 6 7.4 Optics Periscopes Using Plane Mirrors A periscope is an apparatus consisting of a tube attached to a set of plane mirrors or prisms, by which an observer (typically in a submerged submarine or behind a high obstacle) can see things that are otherwise out of sight (Figure 3). Figure 3 In other words, a simple periscope is just a long tube with a mirror at each end.The two mirrors are fitted into each end of the tube at an angle of 45° exactly so that they face each other. L. Bonello Page 7 7.4 Optics Light from a distant object strikes the top mirror and is then reflected at angle of 90° down the periscope tube. At the bottom of the periscope, the light strikes the second mirror and is reflected into the eye ( see Figure 4). Figure 4 L. Bonello Page 8