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Light Reflection and Refraction

Light rays can be change in 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 reflection from a smooth surface, the angle of the reflected ray is equal to the angle of the incident ray.The reflected rays is always in the plane defined by the incident ray.


The Reflection of light


Rays and wave fronts

              The Light is a very complex phenomenon, but in their many situations its behavior can be understood with a simple model based on rays and wave fronts. A ray is a thin beam of light travels in a straight line. A wave front is the line or surface connecting all the light that left a source at the same time. For a source like the Sun, rays radiate out in all the directions; the wave fronts are spheres centered on the Sun. If the source is a long away, the wave fronts can be treated as parallel lines.

               Rays and wave fronts generally can be used to represent light when the light is interacting with objects that are much larger than the wavelength of light, which is about 500 nm. In particular, we will use rays and wave fronts to analyze how light interacts with mirrors and lenses.


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The law of reflection

                Objects can be seen through the light they emit, or, more often, by the light they reflect. Reflected lights are obeys the law of reflection, that the angle of reflection equals the angle of incidence.

               For objects such as mirror, with surfaces so smooth that any hills or valleys on the surface are smaller than the wavelength of light, the law of reflection applies on a large scale. All the light travelling from one direction and reflecting from the mirror is reflected in one direction; reflection from such objects is known as specular reflection.

                Most of the objects exhibit diffuse the reflection, with light being reflected in all directions. All objects obey the law of reflections on a microscopic level, but if the irregularities on the surface of an object are larger than the wavelength of light, which is usually the case, the light reflects off in all directions.


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The Refraction of light


                 When we talk about the speed of the light, we're usually talking about the speed of light in a vacuum, which is 3.00 x 108 m/s. When light travels through the something else, such as glass, diamond, or plastic, it travels at a different speed. The speed of the light in a given material is related to a quantity called the index of refraction, n, which is defined as the ratio of the speed of light in vacuum to the speed of light in the medium:

index of refraction : n = c / v


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