In support of all the students who are displaced from school due to the Corona
virus. Access to physics zone and chemistry zone lessons are now available free
of charge. This will be maintained at least through August 1st 2020. Learn and be well.
Image Formation - Ray Tracing Basics
Wherever two or more light rays from the same point on an object cross or seem
to cross, an image gets formed. For any given mirror or lens, you could pick any two
rays from your object (the thing we are making the image of) and trace them out using a
protractor and possibly some trig. It turns out, that there are three rays that we
can be absolutely sure of without the use of a protractor. Drawing any two of these
known rays can identify where the image is. Pick whichever two rays make the most
sense to you.
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Any ray coming in parallel to the principal axis will
reflect (if it's a mirror) or refract (if it's a lens) through the focal
point (or as though it came from the virtual focus). Keep your wits
about you, light bounces off mirrors and passes through lenses. |
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Any ray coming through the focal point (or seeming to
pass through the virtual focus) will reflect or refract parallel to the
principal axis. |
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Any ray passing through the center of a mirror will
reflect off following the law of reflection. Any ray passing through
the center of a lens will pass straight through without seeming to change
direction. |
| To find the where the
image of an object gets formed, pick your two favorite rays and trace them
for the top of the object. Where the two reflected or refracted rays
cross or seem to cross is where the image of the top of the object is
formed. Repeat the process for the bottom of the object to identify
where the bottom of the image is formed. Once you know where the
bottom and the top is, the rest of the image is between the them. |
