VISUAL PHYSICS ONLINE WAVES RAY MODEL OF LIGHT IMAGE FORMATION: MIRRORS
	For shiny surfaces, such as mirrors, more than 95% of the light may be reflected. When a narrow beam of light falls on a flat surface, the law of reflection is obeyed angle of incidence = angle of reflection This is known as secular reflection. When light is incident on a rough surface (even microscopically rough such as paper), the light is reflected in many directions, but at each small section of the surface the law of reflection holds. This is called diffuse reflection. Because of diffuse reflection in all directions, an ordinary object can be seen from many different angles. When you move your head about, you still receive the light from a small section of the object but the rays have travelled different directions into your eye. Fig. 8. Reflection of the torch light from a piece of paper and a mirror. Th open mesh parabolic dish of a radio telescope is like a diffuse reflector for short wavelength light but acts like a highly polished reflector for long wavelength radio waves. At a microscopic level, paper has rough surface and is a diffuse reflector. The picture shows a magnified view of the surface of a sample of paper. When a narrow beam of light falls on a plane mirror, the light will not reach your eyes unless they are placed in the correct position where the law of reflection is satisfied (figure 8). When you look straight into a mirror, you see what appears to be yourself as well as objects surrounding you. You and the objects appear as if they are in front of you and located behind the mirror. However, what you see in the mirror is called an image. The image formed in the mirror has left and right reversed (figure 8). Fig. 8. A mirror forms an image where left and right are reversed. The mirror image is called a virtual image since the rays of light do not pass through the image location it merely seems as though the light is coming from the image because our brains interpret any light coming into our eyes as having come in a straight-line path in front of us. You cant capture a virtual image on a film by placing it where you think the image is located. A real image can be recorded on a film placed at the location of the image since the light rays actually pass through the image location. From each point on an object light is emitted in all directions. Only the light that travels in a direction such that the law of reflection is satisfied will reach the eye from the mirror. Fig. 9. Formation of a virtual image by a plane mirror. In the reflection of the light rays from the mirror surface, the law of reflection is satisfied (angle of incidence = angle of reflection). The height h of the object and its image are equal. The distance d of the object from the mirror and the distance from the mirror to the virtual image are also equal (object distance = image distance). However, the image is reversed right appears to be left and left appears to be right in image.
VISUAL PHYSICS ONLINE If you have any feedback, comments, suggestions or corrections please email: Ian Cooper School of Physics University of Sydney ian.cooper@sydney.edu.au