Convex mirrors are useful for shop security and rear-view mirrors on vehicles because they give a wider field of vision. Some light is scattered in all directions when it hits very small particles such as gas molecules or much larger particles such as dust or droplets of water.
The amount of scattering depends on how big the particle is compared to the wavelength of light that is hitting it. Smaller wavelengths are scattered more.
Light from the sun is made of all the colours of the rainbow. As this light hits the particles of nitrogen and oxygen in our atmosphere, it is scattered in all directions.
Blue light has a smaller wavelength than red light, so it is scattered much more than red light. When we look at the sky, we see all the places that the blue light has been scattered from. This means that a lot of the blue light has been scattered out well before the light arrives at us, so the sky appears redder. Clouds appear white because the water droplets are much larger than the wavelengths of light.
For this situation, all wavelengths of light are equally scattered in all directions. In Light and sight: true or false? In Investigating reflection students investigate specular and diffuse reflection by looking into a dark box and shining a torch at various objects, coloured paper and a mirror.
To model blue sky and a red sunset, try shining white light from a torch or a projector into a glass container of water with a few drops of milk in it. You should see a blue haze from the sides. If you look to the far end of the container, you should notice the light has a reddish hue. The most amusing applications for curved mirrors are the novelty mirrors found at state fairs, carnivals, and fun houses.
These mirrors often incorporate a mixture of concave and convex surfaces, or surfaces that gently change curvature, to produce bizarre, distorted reflections when people observe themselves. Spoons can be employed to simulate convex and concave mirrors, as illustrated in Figure 4 for the reflection of a young woman standing beside a wooden fence. When the image of the woman and fence are reflected from the outside bowl surface convex of the spoon, the image is upright, but distorted at the edges where the spoon curvature varies.
In contrast, when the reverse side of the spoon the inside bowl, or concave, surface is utilized to reflect the scene, the image of the woman and fence are inverted. An object beyond the center of curvature of a concave mirror forms a real and inverted image between the focal point and the center of curvature.
This interactive tutorial explores how moving the object farther away from the center of curvature affects the size of the real image formed by the mirror. The reflection patterns obtained from both concave and convex mirrors are presented in Figure 5. The concave mirror has a reflection surface that curves inward, resembling a portion of the interior of a sphere. When light rays that are parallel to the principal or optical axis reflect from the surface of a concave mirror in this case, light rays from the owl's feet , they converge on the focal point red dot in front of the mirror.
The distance from the reflecting surface to the focal point is known as the mirror's focal length. The size of the image depends upon the distance of the object from the mirror and its position with respect to the mirror surface. In this case, the owl is placed away from the center of curvature and the reflected image is upside down and positioned between the mirror's center of curvature and its focal point.
The convex mirror has a reflecting surface that curves outward, resembling a portion of the exterior of a sphere. Light rays parallel to the optical axis are reflected from the surface in a direction that diverges from the focal point, which is behind the mirror Figure 5.
Images formed with convex mirrors are always right side up and reduced in size. These images are also termed virtual images, because they occur where reflected rays appear to diverge from a focal point behind the mirror. The manner in which gemstones are cut is one of the more aesthetically important and pleasing applications of the principles of light reflection. Particularly in the case of diamonds, the beauty and economic value of an individual stone is largely determined by the geometric relationships of the external faces or facets of the gem.
The facets that are cut into a diamond are planned so that most of the light that falls on the front face of the stone is reflected back toward the observer Figure 6. A portion of the light is reflected directly from the outside upper facets, but some enters the diamond, and after internal reflection, is reflected back out of the stone from the inside surfaces of the lower facets. These internal ray paths and multiple reflections are responsible for a diamond's sparkle, often referred to as its "fire".
An interesting consequence of a perfectly cut stone is that it will show a brilliant reflection when viewed from the front, but will look darker or dull from the back, as illustrated in Figure 6. Light rays are reflected from mirrors at all angles from which they arrive. In certain other situations, however, light may only be reflected from some angles and not others, leading to a phenomenon known as total internal reflection.
This can be illustrated by a situation in which a diver working below the surface of perfectly calm water shines a bright flashlight directly upward at the surface. If the light strikes the surface at right angles it continues directly out of the water as a vertical beam projected into the air.
If the light's beam is directed at a slight angle to the surface, so that it impacts the surface at an oblique angle, the beam will emerge from the water, but will be bent by refraction toward the plane of the surface.
The angle between the emerging beam and the surface of the water will be smaller than the angle between the light beam and the surface below the water. If the diver continues to angle the light at more of a glancing angle to the surface, the beam rising out of the water will get closer and closer to the surface, until at some point it will be parallel to the surface.
Because of light bending due to refraction, the emerging beam will become parallel to the surface before the light below the water has reached the same angle. The point at which the emerging beam becomes parallel to the surface occurs at the critical angle for water. If the light is angled still further, none of it will emerge. Instead of being refracted, all of the light will reflect at the water's surface back into the water just as it would at the surface of a mirror.
Regardless of the position of the object reflected by a convex mirror, the image formed is always virtual, upright, and reduced in size. This interactive tutorial explores how moving the object farther away from the mirror's surface affects the size of the virtual image formed behind the mirror. The principle of total internal reflection is the basis for fiber optic light transmission that makes possible medical procedures such as endoscopy, telephone voice transmissions encoded as light pulses, and devices such as fiber optic illuminators that are widely used in microscopy and other tasks requiring precision lighting effects.
The prisms employed in binoculars and in single-lens reflex cameras also utilize total internal reflection to direct images through several degree angles and into the user's eye. In the case of fiber optic transmission, light entering one end of the fiber is reflected internally numerous times from the wall of the fiber as it zigzags toward the other end, with none of the light escaping through the thin fiber walls.
This method of "piping" light can be maintained for long distances and with numerous turns along the path of the fiber. Total internal reflection is only possible under certain conditions. The light is required to travel in a medium that has relatively high refractive index, and this value must be higher than that of the surrounding medium.
Water, glass, and many plastics are therefore suitable for use when they are surrounded by air. If the materials are chosen appropriately, reflections of the light inside the fiber or light pipe will occur at a shallow angle to the inner surface see Figure 7 , and all light will be totally contained within the pipe until it exits at the far end.
At the entrance to the optic fiber, however, the light must strike the end at a high incidence angle in order to travel across the boundary and into the fiber.
The principles of reflection are exploited to great benefit in many optical instruments and devices, and this often includes the application of various mechanisms to reduce reflections from surfaces that take part in image formation. There are many different types of mirrors, and each behaves somewhat differently. The most common type is a silver mirror, consisting of a thin layer of silver on the bottom side of a glass slide.
Additional layers of copper or other materials may be deposited on the back side of the silver layer, but these layers are not relevant for the optical properties. To understand how such mirrors work, let us first describe the interaction of light with some media in the semiclassical view. Light consists of electromagnetic waves, which induce some oscillation of electrons in any substance hit by the light.
In an insulator such as glass, the electrons are firmly bound and can only oscillate around their normal position. This movement influences the propagation of light so that its wave velocity is reduced, while there is only a small loss of energy.
This is different in a metal, where some of the electrons are free to move over large distances, but their motion is damped so that energy is dissipated.
The wave amplitude decays very quickly in the metal--usually within a small fraction of the wavelength. Associated with that decay is a loss of energy in the wave and some heating of the metal. In other words, the power is transferred to another wave with a different propagation direction opposite to the original direction for normal incidence on the surface.
In the case of a silver mirror, this reflection occurs at the interface of glass to silver, essentially because the optical properties of the metal are very different from those of glass. As a general rule, waves experience significant reflection at interfaces between media with substantially different propagation properties. In the end we obtain a reflected wave with essentially the same properties as the incident wave apart from some loss of power, which typically amounts to a few percent for silver mirrors.
This reflection loss does not matter for a mirror used in the bathroom, but such metallic mirrors are usually not suitable for use in lasers. The loss of light itself is often unacceptable, and the associated heating of the mirror can cause difficulties, in particular via thermally induced deformations.
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