Vocabulary Answers
Section 22.1
1. incandescent
2. intensity
3. fluorescent
Section 22.2
4. photoreceptors
5. additive process
6. cones
7. white light
8. color
9. additive primary colors
10. rods
Section 22.3
11. CYMK color process
12. subtractive process
13. RGB color process
14. subtractive primary colors
Reviewing Concepts
Section 22.1
1. An incandescent bulb generates light and also a great deal of heat. A
fluorescent bulb generates light and only a small amount of heat.
2. We see lightning before we hear thunder because light travels much
faster than sound.
3. b) acceleration
4. To make light, fluorescent bulbs use high-voltage electricity to excite
atoms of gas that fill the bulb. The atoms of gas, as a result, release
ultraviolet light that we cannot see. However, the ultraviolet light
excites the atoms (of phosphorous) in the white coating of the bulb.
The atoms in the coating then emit visible light.
5. A black piece of cloth with absorb all colors of the visible light
spectrum. This means that very little or no light is reflecting to your
eyes off of the surface. In contrast, a white piece of cloth reflects all
colors of visible light. The mixture of all colors of visible light is
white light.
6. Reflection is the bouncing of light off a surface. Refraction is the
bending of light when it moves from one material into another
material.
Section 22.2
7. White light is the combination of all the possible colors of light.
8. The color of an object is based on its material and how the object
reflects or absorbs light. Color is also based on the composition of the
light shining on the object, and your brain’s interpretation of color.
9. Red, green, and blue
10. Red has the least energy; blue has the most energy.
11. Rods respond to differences in intensity and detect black, white, and
shades of gray. Rods are more sensitive to light than cones. Cones
respond to color. In dim light, the cones do not have enough light to
respond to color, and most of your vision comes from the rod cells.
So, in dim lighting, your vision tends to be black and white.
Section 22.3
12. Answers are:
a. True
b. True
c. False; Absorbs
d. False. Reflects.
13. Magenta, cyan, and yellow
14. More colors are subtracted from the light and absorbed by the paint.
15. Pigments work by absorbing specific colors from white light, which
is a mixture of all the colors. When you add pigments together in a
mix, they take away (absorb), or subtract, more colors from the white
light.
16. Red and blue are reflected by magenta.
17. Impurities in the pigments result in a muddy gray color when cyan,
magenta, and yellow are mixed. A purer black color can be obtained
when black pigment is used. In addition, ink is expensive, so mixing
three separate ink colors would use three times the ink as printing
with black ink.
18. The printing press uses the CMYK process (subtractive color
process), mixing cyan, magenta, yellow, and black pigments to
produce the colors of the picture.
19. The television screen uses the RGB process (additive color process),
mixing red, blue, and green dots of light (or pixels) to produce the
light seen on the screen.
20. Since the computer monitor makes its own light, the image on the
screen is created with the RGB color process and uses red, green, and
blue light in different combinations to make all the colors in the
image. This is the additive color process. The image on the paper is
created using the CMYK color process and uses cyan, magenta,
yellow, and black colored inks in different combinations to make all
the colors in the image. This is the subtractive color process.
Solving Problems
Section 22.1
1. Answers are:
a. Light intensity is measured in units of power per area.
b. If the intensity of light at 1 meter from a source is 1 W/m2, it will
be 0.25 W/m2 at 2 meters from the source. (1 W/m2 ÷ 4 = 0.25
W/m2)
c. At 1 meter from a light source, a 1 m2 area has a light intensity
of 0.8 W/m2. At 3 meters from a light source, a 1 m2 area will
have a light intensity that is 0.09 W/m2 (0.8 W/m2 ÷ 9 = 0.09 W/
m2)
2. Light intensity is inversely proportional to the square of the distance
from the source. The light two meters away will be 1/4 the intensity
of the light one meter away.
3. (4 sec) × (0.21 miles/sec) = 0.84 miles
4. Light waves, sound waves, water waves
Section 22.2
5. Blue light has more energy than red light, so the blue star would be
hotter.
6. Answers are:
a. magenta
b. cyan
c. yellow
d. white
7. Magenta light is a mixture of red and blue light. Green light is a
primary color of light. If you mix magenta and green light, you get a
combination of red, blue, and green light which makes white light.
Section 22.3
8. Table filled in:
9. yellow and cyan
10. Answers are:
a. magenta + yellow
b. yellow + cyan
c. magenta + cyan
d. no pigments
11. Blue
12. Answers are:
a. RGB
b. RGB
c. CMYK
d. RGB
13. Answers are:
a. Red and blue light
b. Green light
c. Pigments in a plant reflects green light, so the plant will not
absorb enough energy if placed in green light. But the plant
pigments absorb and use red and blue light, so the plant grows
faster if placed in white light which contains both those colors of
light.
d. Since plants need light to grow, it is useful for them to have
additional pigments to help capture light. This is why plants
have green and other pigments of color. However, if plants could
absorb all visible light, they would probably get too hot.
Therefore, it is important that plants reflect some light that falls
on their leaves.
Applying Your Knowledge
Section 22.1
1. Answers are:
a. Students should ask the question to 20 people they know and
record the number of yes and no answers.
b. The correct answer is “no, it is not possible to see your hand in
front of your face in a completely dark room.” The number of
“yes” and “no” answers to this questions will help students see
whether this misconception about how we see is common among
people they know.
c. Students should make a simple flyer that explains that seeing an
object depends on the presence of light reflecting off an object or
being produced by the object. Objects cannot be seen if there is
no visible light present.
2. Most incandescent bulbs are filled with argon gas. Halogen bulbs,
however, are filled with a halogen gas. When the tungsten filament
burns in an incandescent bulb, carbon is produced. The halogen gas in
the halogen bulb helps re-deposit the carbon back on the filament.
This process makes it possible to burn the tungsten filament at a
higher temperature so that it can produce brighter and whiter light per
watt of the bulb. Halogen bulbs tend to be more efficient than regular
incandescent bulbs because they can be smaller and last longer than
similarly sized regular incandescent bulbs.
3. t = d ÷ v
The speed of sound in air equals 340 m/sec
The speed of light, c, equals 300,000,000 m/sec (3 × 108 m/sec)
For sound:
t = (1,609 m) ÷ (340 m/sec) = 4.73 seconds
For light:
t = (1,609 m) ÷ (300,000,000 m/sec)
= 0.0000054 seconds (5.4 × 10-6 m/sec)
4. d = vt
The speed of light, c, equals 300,000,000 m/sec (3 × 108 m/sec)
One year = (365 days/yr)(24 hrs/day)(60 min/hr)(60 sec/min)
= 31,500,000 sec (3.15 × 107 sec)
d = (3 × 108 m/sec)(3.15 × 107 sec) = 9.45 × 1015 meters
Section 22.2
5. Example answer: The human eye is most sensitive to yellowish-green
light, then red light, and then blue light. Given this information, it is
important that yellow-green be used as a color for objects that are
involved in emergency situations. These objects need to be responded
to quickly. For example, it is important for motorists to see a fire
engine quickly so that he or she can move out of the way. However,
since humans are second most sensitive to red light, I don’t think the
color of fire engines need to be changed from red to yellow-green.
6. Almost all the photoreceptors in the eyes of nocturnal animals are
rods, enabling them to be more sensitive to low levels of light. They
usually have very few, if any, cones. As a result, most nocturnal
animals see in black and white, not in color.
7. You see blue light because the blue pigment in the filter absorbs all
the other colors but blue. Blue light passes through (or is transmitted
by) the filter.
8. Fluorescent light is made up of more blue light, and incandescent
light is made up of more yellow light. This affects the light available
for the clothes to absorb and reflect and therefore the clothes look
different in the store than at home.
9. Project responses will vary. Some examples of devices or products
that students could improve include: traffic lights, swimming pool
water quality tests, thermometers, and any device that uses color
coding. Have students make a diagram or model of the improved
product they designed. Students could also make informational
brochures to raise awareness about color blindness.