Shinwari,Mariam,Ivan text:

Law of Reflection

"Reflection is a change in direction of a wave upon striking the interface between two materials."(#1.)

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For example, in image 4, the eye is sighting along a line at a position above the actual image location. For light from the object to reflect off the mirror and travel to the eye, the light would have to reflect in such a way that the angle of incidence is less than the angle of reflection. In Diagram B above, the eye is sighting along a line at a position below the actual image location. In this case, for light from the object to reflect off the mirror and travel to the eye, the light would have to reflect in such a way that the angle of incidence is more than the angle of reflection. Neither of these cases would follow the law of reflection. In fact, in each case, the image is not seen when sighting along the indicated line of sight. It is because of the law of reflection that an eye must sight at the image location in order to see the image of an object in a mirror.

Total Internal Reflection

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: 

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<ac:structured-macro ac:name="anchor" ac:schema-version="1" ac:macro-id="90117257007b3298-ddbd526b-41854616-88799a7b-b4325c57cadf3826c574880d"><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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