CHAPTER INVESTIGATION
Temperature, Brightness,
and Color
OVERVIEW AND PURPOSE Think of the metal heating
MATERIALS
surface on a hot plate. How can you tell whether the hot plate is
fully heated? Is the metal surface brighter or dimmer than when
it is just starting to get warm? Does the color of the surface
change as the hot plate gets hotter? You may already have an
idea of how temperature, brightness, and color are related—at
least when it comes to heated metal. Do the same relationships
apply to electric lights? to stars? This investigation is designed to
help you find out. You will
• construct a wax photometer to compare the brightnesses
and colors of different light sources
• determine how the temperature of a light source affects its
brightness and color
Problem
• 2 paraffin blocks
• aluminum foil
• 2 rubber bands
• 2 light-bulb holders
• 2 miniature light bulbs
• 3 AA batteries
• 4 pieces of uninsulated
copper wire 15 cm long
• masking tape
for Challenge:
• incandescent lamp
• dimmer switch
Write
It Up
How are brightness and color related to temperature?
Hypothesize
Write
It Up
Write a hypothesis to explain how brightness and color are
related to temperature. Your hypothesis should take the form of
an “If . . . , then . . . , because . . .” statement.
Procedure
An instrument called a photometer makes it easier to compare
the brightnesses and colors of different light sources. Assemble
the wax photometer as shown on page 785. The aluminum foil
between the wax blocks should be folded so that the shiny side
faces out on both sides.
Hold the photometer so that you can see both blocks. Bring it
to different locations in the classroom, and observe how the
brightnesses and colors of the blocks change as the two sides of
the photometer are exposed to different light conditions.
Tape a piece of copper wire to each end of a
battery, and connect the wires to a light-bulb
holder. The battery will provide electricity to
heat up the wire inside a light bulb.
784 Unit 6: Space Science
step 3
Tape the negative terminal, or flat end, of one
battery to the positive terminal of another
battery. Tape a piece of copper wire to each end,
and connect the wires to
a light-bulb holder.
Because two batteries
will provide electricity
to the bulb in this
holder, the wire in
the bulb will be
hotter than the wire
in the bulb powered
by one battery.
step 4
With the room darkened, insert a bulb into each
light-bulb holder. If the bulb connected to two
batteries does not light up, you may need to press
the two batteries together with your fingers.
Place the photometer halfway between the two
light bulbs. Compare the brightnesses of the two
light sources. Record your observations in your
Science Notebook.
Move the photometer closer to the cooler bulb
until both sides of the photometer are equally
bright. Compare the colors of the two light
sources. Record your observations in your
Science Notebook. To avoid draining the
batteries, remove the bulbs from the holders
when you have completed this step.
Observe and Analyze
Write
It Up
1. RECORD OBSERVATIONS Draw the
setup of your photometer and light sources.
Be sure your data table is complete with
descriptions of brightness and color.
2. IDENTIFY Identify the variables
in this experiment. List them in
your Science Notebook.
Write
Conclude
It Up
1. INTERPRET Answer the question in
the problem. Compare your results with
your hypothesis.
2. ANALYZE How does distance affect your
perception of the brightness of an object?
3. APPLY Judging by the results of the investigation, would you expect a red star or a
yellow star to be hotter? Explain why.
INVESTIGATE Further
CHALLENGE Connect an incandescent lamp
to a dimmer switch. Write a procedure to show
how you would use a photometer to show the
relationship between the color and the temperature of the bulb as it fades from brightest to
dimmest. Then carry out your procedure.
step 6
olor
ightness, and C
Temperature, Br
nalyze
Observe and A
s of Light from
Table 1. Propertie
Two Sources
Cooler Bulb
(one battery)
Warmer Bulb
(two batteries)
Brightness
Color
Chapter 22: Stars, Galaxies, and the Universe 785