Can you name this wave phenomena?







Interference or beats



B. Reflection





[ Reflection ]

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St. Mary's Physics


1. Law of Reflection

a.  θ of incidence = θ of reflection



[ θin = θref ]

[ HTML5 ]
St. Mary's Physics




Use the acute angles on your protractor /p>

Charles William Weick Elementary Mechanical Drawing, Theory and Practice
(New York: McGraw-Hill Book Company, 1915) 21

ETC Clipart  | Protractor

Line going through O, we will
 refer to as the baseline 






θin = θincidence
(angle incoming normal ray
 makes with the normal)

θref = θreflect
(angle reflected light makes with the normal)

Ray Diagram  - Reflection








Remember ...

... reflection always makes a V





What is the smallest mirror
you need to see your whole body?




1/2 your height



Click and Drag Gecko 

[ Flash ]


The image from a plane mirror:



a. Virtual (realistic) & Upright (Straight up and down)


[ Flash ]









b. Incident ray, normal line, and reflected rays are all in the same plane


Source: Elroy M. Avery School Physics (New York: Sheldon and Company, 1895) 77 

Clipart ETC


c. The distance the object is in front of the mirror equals the distance the image is behind the mirror



2. Two Basic Kinds of Reflection


a. Regular Reflection – reflection off a polished surface (produces images)


Regular Reflection Produces Images


b. Diffuse Reflection – reflection off an irregular surface causing light to scatter (no image)







Which letter correctly

shows reflection?








Ray C







Angle of Reflection?



June 2009







60 degrees
(Angle from normal)


Dr. Carlson - Purdue University








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