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1. #Reflection
2. #Total Internal Reflection
3. #Dispersion
4. #Refraction
4 5. #References
Reflection
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"Reflection is a change in direction of a wave upon striking the interface between two materials."(#1.)
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Total Internal Reflection
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is a phenomena which occurs when light propagates from the medium with greater index of refraction in the medium with lower index of refraction. From Snell's law we know that the light in this case refracts away from the normal. That means that there is an angle of incidence for incoming ray where all the light will not leave the medium with higher index of refraction, but instead it will reflect in direction perpendicular to the normal (i.e. in the plane of the boundary). If the angle of incidence is larger than this critical angle, all the light is reflected back into the medium with higher index of refraction. We can obtain value for critical angle mathematically using following equation:
Where n2 is index of refraction of the medium with higher lower index.
Fig. 5. Multiple total internal reflections (#4.)
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Practical Use of Total Internal Reflection
Total internal reflection has many practical uses. The best known are arguably its use in glass prisms in binoculars and cameras where it allows for compact size of the instrument while providing for long internal optical paths. Second major area of application is in optical cables - namely in multimode optical cables. There the pure glass/silica core is made of material with higher refractive index than the cladding that surrounds it and so the light which enters it under angle of incidence larger than critical it will reflect there and back thorough the cable to the other end (in the same way as on the picture above). This is used extensively in data communications as optical cables offer higher bandwidth (lower attenuation of high frequency signals), resistance to electromagnetic noise and (much) thinner cables. Optical cables are also used in endoscopes (stomach sonds). Other uses are for example in inkless fingerprint readers.
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Dispersion of Light
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The index of refraction of medium is dependent on the frequency of incoming light ray. Therefore if light with with wide frequency spectrum (such as daylight) enters for example glass prism, the component frequency bands (for visible colors) will diffract under slightly different angles. The result is light divided into colorful "strip" for each of basic colors. The very same effect is behind rainbow which is natural occurrence of dispersion.
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Practical Use of Dispersion
Dispersion is used in spectrometers - devices which are used in many fields of science to analyze the chemical composition of objects. It is based on the fact that different chemical elements emit and absorb different wavelenghts of light, and this spectra can be seen using spectrometers.
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Refraction
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It’s the change in direction of a wave due to a change in its medium. It is essentially a surface phenomenon. This is most commonly observed when a wave passes from one medium to another at any angle other than 90° or 0°. (#6.)
Explanation:
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- First video explains shortly speed of light in different mediums.
- Second video gives a brief description of how and why refraction happens.
References:
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#Back to top
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<ac:structured-macro ac:name="anchor" ac:schema-version="1" ac:macro-id="36a98c218443a567-95c8ae50-44d34bbf-94678b78-10f5bea194cebb3c125956ed"><ac:parameter ac:name="">3.</ac:parameter></ac:structured-macro> 3. _Reflection and Its Importance_. (n.d.). Retrieved December 10, 2012, from Physics Classroom: \[http://www.physicsclassroom.com/class/refln/u13l1c.cfm\] |
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9. Lally, S. (2012, October 25). Reflection and Refration . Retrieved December 10, 2012, from How Things Work - Towson University Physics 103: http://howthingsworkclass.blogspot.fi/2012/10/reflection-and-refration-reflection.html (