Ch. 18-19 review
Period:
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ANSWER KEY
1. What colors of pixels are all images on your computer made out of?
red, blue, and green
2. Draw the Venn diagram for the colors of light.
3. Besides black, what are colors of ink are used in standard color inkjet printers?
magenta, and yellow
4. Draw the Venn diagram for the colors of pigments
cyan,
5. Find what the following objects will look like:
a. red object under magenta light
red  blue of light is absorbed by the pigment
b. cyan object under magenta light blue  red from light is absorbed, no green hits obj
c. cyan object under red light black  red from light is absorbed, no G or B hits obj
d. green object under yellow light
green  red from light is absorbed, no B hits obj
6. 100% red ink is mixed with an equal amount of 100% blue ink, what color does your eye see
on the page and why?
black, because the R ink absorbs G&B and reflects only R, B ink
absorbs R&G and reflects only B, so R, G, and B are all absorbed, leaving no color (black)
7. Explain why is the old adage “yellow and blue makes green” not truly accurate.
True yellow reflects G and R to your eye but absorbs B, B absorbs R & G and only reflects B.
So the B absorbs the R&G and the yellow absorbs the B. leaving no light reflected.
8. What is the law of reflection?
Angle of incidence is equal to the angle of reflection.
9. What is the difference between a real and a virtual image?
A real image appears where light rays actually meet and can be projected onto a screen, a
virtual image appears where light rays seem to come from and cannot be projected onto a
screen.
10. Accurately (using ruler and protractor) draw in the “field of view” for each person, use a
different shading style for each person, and determine which where an object would have to be
to be seen by both people in the mirror.
Mirror surface
11. If in a certain flat, handheld mirror, ½ of your face takes up the whole mirror. If you stand
further back, do you see more, less, or the same amount of yourself in the mirror? Draw
diagrams to illustrate this idea.
Standing further back has little effect, because the angle of incidence is always equal to the
angle of reflection, and the further away the object is the smaller the angle of incidence so the
range stays the same
12. How big does a plane mirror need to be to see your whole body in the mirror?
It must be at least half your height to see your whole body
13. Using ray diagrams, find the image formed by the object (the arrow) in the following concave
and convex mirrors. Describe the image as real or virtual, magnified or reduced, and rightside-up or up-side-down.
Real, inverted,
reduced
Virtual, rightside-up,
magnified
Virtual, right-sideup, reduced