Find Monday's Recorded Zoom Session HERE

Audio only is HERE



OPENING QUESTIONS: Sketch an example of "retroreflection" using either a circle or a square (that *should* make sense after yesterday's class)


LEARNING TARGET: I will be able to use the Law of Reflection to calculate the angle in which a light way is reflected from one or more mirrors after today's class.



    • Reflection ("Light waves bouncing off an object")
    • Emission ("Light is given off by an object")
    • Absorption ("Some wavelengths of light are absorbed by an object")
    • Angle of Incidence ("The angle a light ray takes as it moves toward a reflecting surface")
    • Angle of Reflection ("The angle a light ray takes as it moves away from a reflecting object")
    • Retroreflection ("incident light waves are 'double bounced' back to the observer, regardless of the angle of incidence")


Discussion of the Law of Reflection

Perhaps the most basic of all the laws of optics is the Law of Reflection:

"The angle of incidence equals the angle of reflection"


Notice that the angles are each measured in reference to the NORMAL (perpindicular) line

The law of reflection can and often is written mathematically as follows:

θ1 = θ1'

and pronounced as "theta one = theta one prime" to emphasize the sameness of the angles.

To make life a bit easier for us I will often replace that with

θi = θr

to emphasize the angle of incidence = the angle of reflection


Retroreflection is SUPER helpful in our day-to-day life.

It acts so that any light falling on the first surface is "double bounced" off of a second surface and returned back to the light source... REGARDLESS of angle of incidence.

Retroreflection is done using either a cubic or spherical surface...

Now please (*GASP*) bust out your forbidden electronic devices and find yourself a protractor app! We've had good luck with the Keuwlsoft App (Android), PhotoProtractor (Apple)

Moving Right along-- please download this light ray practice