Light Basics and Geometrical Optics
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This text is meant to accompany class discussions. It is not everything there is to know about uniform circular motion. It is meant as a  prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations. See the links below.

This is beginning to discuss an area of light that is refered to as "Optics."  Many poeple think Newton had a lot to do with the discovery of the field of optics. Another misconception was that Galileo Galilei discovered lenses or he created the telescope. He did not, he improved the telescope's lens. That allowed him to see the heavens more than 6 times more clearly than anybody before him. The telescope's was inventor is widely disputed. The father of optics is Abu Ali al Hasan, Arab Muslim scholar Ibn Al-Haytha. To the west he is often referred to as "Alhazen." Alhazen was born in 965, in southern Iraq. This was about 600 years before Newton was born.

 

Ray Tracing
 
Vocabulary


Light reflects off of a body to make the body an "object" and a source of light for all images.

 

If object is underneath the line and pointing downwards, then the upright and inverted image labels would switch.

When you look into a flat mirror on the wall, it appears as if the image is on the other side of the wall. (That is why there are so many kitten and puppy videos of animals reacting to their images in the mirror. https://youtu.be/4dmkRsBm5ww -this is not my video.) This image is a virtual image because light does not pass through the image itself since it looks like it is formed on the other side of the mirror.


Every image is "magnified." Its variable is "M." For right now we will not get into al of the math. Magnifications can be either positive or negative. For now we will look only at the absolute value of the magnification. Conceptually here is what the various M values represent.

M < 1 Image's height looks shorter than the object. Ex: M=0.2, M=0.5, M=0.7
M = 1 Image's height looks the same as the object. Ex: M=1
M > 1 Image's height looks taller than the object. Ex: M=1.5, M= 3.4, M=14.5

 

Ray tracing for a plane mirror

 

Light from the room bounces off the dog's eyes and goes in all different directions. This diagram will first look at one ray that leave the dogs eye and is incident on the mirror at a 45 degree angle. Due to the law of reflection the light rays bounces off the mirror at a 45 degree angle. The ray that bounces off the mirror is called the reflected ray. This ray is extended on a straight line on the back side of the mirror where no light exists. This is the virtual ray because it exists in virtual space.

 

A second ray is incident on the mirror at a 90 degree angle. It bounces back on itself to the left. It too is extended into the virtual space. Where these two rays meet is where the dog's eye will be seen.

This is important. Where any two reflected rays, either real or virtual, intersect, is the location of the object.

 
Concave Mirrors


See each step ray by ray
  • Video
  • Ray by Ray Still Images

The video below describes how to draw the 4 rays for a convcave mirror. The image is found where the REFLECTED rays cross.

This video can be found on YouTube at https://youtu.be/v9DwvFb1bzA

These steps are the same for both concave and convex mirrors.

 

 

Convex Mirrors


See each step ray by ray
  • Video
  • Ray by Ray Still Images

The video below describes how to draw the 4 rays for a convex mirror. The image is found where the REFLECTED rays cross.

The steps for draing the 4 rays for convex mirrors are the same steps that are used for convex mirrors.

Before answer the quiz below you should work on this ray tracing worksheet.


by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)

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