Reflections and Refractions
Assume that light waves encounter the plane surface of a piece of glass after traveling initially through air as shown in the figure to the right. What happens to the waves as they pass into the glass and continue to travel through the glass? The speed of light in glass or water is less than the speed of light in a vacuum or air.
Typical values for the index of refraction of glass are between 1. The distance between wave fronts will therefore be shorter in the glass than in air, since the waves travel a smaller distance per period T. Now consider wave fronts and their corresponding light rays approaching the surface at an angle. We can see that the rays will bend as the wave passes from air to glass. The bending occurs because the wave fronts do not travel as far in one cycle in the glass as they do in air.
As the diagram shows, the wave front halfway into the glass travels a smaller distance in glass than it does in air, causing it to bend in the middle. Thus, the ray, which is perpendicular to the wave front, also bends. The situation is like a marching band marching onto a muddy field at an angle to the edge of the field. The rows bend as the speed of the marchers is reduced by the mud. The amount of bending depends on the angle of incidence and on the indices of refraction of glass and air, which determine the change in speed. Reflection Reflection is the abrupt change in the direction of propagation of a wave that strikes the boundary between two different media.epay.vg/how-to-put-a-tracking-device-on-a-cellphone-oppo.php
Difference Between Reflection and Refraction
Specular reflection occurs at smooth, plane boundaries. This is Snell's law , or the law of refraction.
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When light passes from one transparent medium to another, the rays are bent toward the surface normal if the speed of light is smaller in the second medium than in the first. The rays are bent away from this normal if the speed of light in the second medium is greater than in the first. The picture on the right shows a light wave incident on a slab of glass.
Reflection, Refraction, and Diffraction
One part of the wave is reflected, and another part is refracted as it passes into the glass. The law of reflection states that, on reflection from a smooth surface, the angle of the reflected ray is equal to the angle of the incident ray. By convention, all angles in geometrical optics are measured with respect to the normal to the surface—that is, to a line perpendicular to the surface. The reflected ray is always in the plane defined by the incident ray and the normal to the surface. The law of reflection can be used to understand the images produced by plane and curved mirrors.
Unlike mirrors, most natural surfaces are rough on the scale of the wavelength of light, and, as a consequence, parallel incident light rays are reflected in many different directions, or diffusely. Diffuse reflection is responsible for the ability to see most illuminated surfaces from any position—rays reach the eyes after reflecting off every portion of the surface.
When light traveling in one transparent medium encounters a boundary with a second transparent medium e. As the transmitted light moves into the second medium, it changes its direction of travel; that is, it is refracted. The index of refraction for any medium is a dimensionless constant equal to the ratio of the speed of light in a vacuum to its speed in that medium. By definition, the index of refraction for a vacuum is exactly 1. Because the speed of light in any transparent medium is always less than the speed of light in a vacuum, the indices of refraction of all media are greater than one, with indices for typical transparent materials between one and two.
For example, the index of refraction of air at standard conditions is 1. The amount of bending of a light ray as it crosses a boundary between two media is dictated by the difference in the two indices of refraction. When light passes into a denser medium, the ray is bent toward the normal.
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Conversely, light emerging obliquely from a denser medium is bent away from the normal. In the special case where the incident beam is perpendicular to the boundary that is, equal to the normal , there is no change in the direction of the light as it enters the second medium. Light rays passing through a lens are bent at both surfaces of the lens.
With proper design of the curvatures of the surfaces, various focusing effects can be realized. For example, rays initially diverging from a point source of light can be redirected by a lens to converge at a point in space, forming a focused image.
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The optics of the human eye is centred around the focusing properties of the cornea and the crystalline lens. Light rays from distant objects pass through these two components and are focused into a sharp image on the light-sensitive retina. Other optical imaging systems range from simple single-lens applications, such as the magnifying glass, the eyeglass, and the contact lens , to complex configurations of multiple lenses.
It is not unusual for a modern camera to have a half dozen or more separate lens elements, chosen to produce specific magnifications, minimize light losses via unwanted reflections, and minimize image distortion caused by lens aberrations. We welcome suggested improvements to any of our articles.
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Reflection and refraction Light rays change direction when they reflect off a surface, move from one transparent medium into another, or travel through a medium whose composition is continuously changing. Previous page Light rays. Page 4 of Next page Total internal reflection. Learn More in these related Britannica articles: Visible light is the most familiar form of electromagnetic radiation and makes up that portion of the spectrum to which the eye is sensitive.