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- Reflection. Reflection is when incident light (incoming light) hits an object and bounces off. Very smooth surfaces such as mirrors reflect almost all incident light.
- Absorption. Absorption occurs when photons from incident light hit atoms and molecules and cause them to vibrate. The more an object's molecules move and vibrate, the hotter it becomes.
- Diffraction. Diffraction is the bending and spreading of waves around an obstacle. It is most pronounced when a light wave strikes an object with a size comparable to its own wavelength.
- Scatter. Scattering occurs when light bounces off an object in a variety of directions. The amount of scattering that takes place depends on the wavelength of the light and the size and structure of the object.
Light rays and ray diagrams. Light travels in a straight line. When drawing a light ray: Use a ruler and a sharp pencil to draw a straight line. Add an arrow to show the direction the light is ...
- Overview
- 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. 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.g., air and glass), a portion of the light is reflected and a portion is transmitted into the second medium. As the transmitted light moves into the second medium, it changes its direction of travel; that is, it is refracted. The law of refraction, also known as Snell’s law, describes the relationship between the angle of incidence (θ1) and the angle of refraction (θ2), measured with respect to the normal (“perpendicular line”) to the surface, in mathematical terms: n1 sin θ1 = n2 sin θ2, where n1 and n2 are the index of refraction of the first and second media, respectively. 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 1.0003, water is 1.33, and glass is about 1.5.
The basic features of refraction are easily derived from Snell’s law. 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. 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 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. 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.g., air and glass), a portion of the light is reflected and a portion is transmitted into the second medium. As the transmitted light moves into the second medium, it changes its direction of travel; that is, it is refracted. The law of refraction, also known as Snell’s law, describes the relationship between the angle of incidence (θ1) and the angle of refraction (θ2), measured with respect to the normal (“perpendicular line”) to the surface, in mathematical terms: n1 sin θ1 = n2 sin θ2, where n1 and n2 are the index of refraction of the first and second media, respectively. 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 1.0003, water is 1.33, and glass is about 1.5.
The basic features of refraction are easily derived from Snell’s law. 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. 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.
Jun 7, 2023 · Reflection and refraction can work together — often with awesome results. Consider the bending of the sun’s light as it passes through Earth’s atmosphere at a low angle. This tends to happen at sunrise or sunset. Sunlight’s bending, or refracting, paints clouds near the horizon in an array of red and orange hues.
The light ray model makes the assumption that light travels in a straight line through transparent media such as air or water. The model also assumes that light rays behave in a predictable manner when they encounter surfaces such as an interface between different media (air and water for example) or the surface of an opaque object.
William Harris & Craig Freudenrich, Ph.D. "How Light Works" 1 January 1970. Some of the brightest minds in history have focused their intellects on the subject of light. Einstein even tried to imagine riding on a beam of light. We won't get that crazy, but we will shine a light on everything scientists have found so far.
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When light strikes a rough surface, incoming light rays reflect at all sorts of angles because the surface is uneven. This scattering occurs in many of the objects we encounter every day. The surface of paper is a good example. You can see just how rough it is if you peer at it under a microscope. When light hits paper, the waves are reflected ...
