How does the temperature of a ‘Blackbody effect the maximum wavelength of light it gives
off?
Website for virtual Blackbody Simulation Lab:
http://phet.colorado.edu/sims/blackbody-spectrum/blackbody-spectrum_en.html
Background: A “blackbody” is an object that does not reflect light, it only gives off (emits) light! Of course
in order for any object to emit light it must get hot and glow. In this lab you are going to observe the
distribution of light (EM Radiation) given off by hot objects and determine if there is an empirical
relationship between an object’s temperature and the EM Radiation emitted.
All objects with a temperature above absolute zero (0 kelvin) emit radiation. The peak emission of this
radiation depends on the temperature.
Figure 1
The following questions refer to Figure 1
1. In which direction is the frequency or energy of the electromagnetic waves increasing in Figure 1?
A. To the right
B. To the left
2. What do we call the area immediately to the left of the visible spectrum in Figure 1?
A. Infrared
B. X-ray
C. Microwave
D. Ultraviolet
3. What do we call the area immediately to the right of the visible spectrum in Figure 1?
A. Infrared
B. X-ray
C. Microwave
D. Ultraviolet
Figure 2
4. The graph above represents the electromagnet spectrum for a light bulb at 3045 K. What is the
approximate peak wavelength for this temperature from the graph? (Note the scale goes from 0 to 3 µm
in 1 µm (major division) increments.
A. 1000 nm
B. 1000 um
C. 3 nm
D. 0.5 um
5. The human body has a temperature of approximately 310 K. Find the approximate peak wavelength of
this temperature by doing the following:
1. Enter 310 (body temperature in Kelvin) into the temperature field
2. Adjust the intensity zoom in the positive direction (zoom in) - more sensitivity
3. Adjust the wavelength zoom in the negative direction (zoom out) - wider wavelength view
A. 24 um
B. 940 nm
C. 9.4 um
D. 5 um
Part I Characteristics of the blackbody spectrum emitted from an incandescent light bulb.
Set the temperature of the blackbody to 3000 K. (This can be accomplished by simply typing in the
temperature.) This is approximately the temperature of the tungsten filament in an incandescent light
bulb which is a good black body. Adjust the axis zoom tools to observe a large peak; 3.16 on the vertical
axis and 3 on the horizontal axis. Understand the labels of each axis! On the vertical axis is intensity; the
amount (or strength) of light given off. On the horizontal axis is the wavelength of all EM Radiation
emitted; including the visible light given off.
1. Based on the graph, describe the intensity and distribution of EM Radiation (Electromagnetic output)
produced by the glowing tungsten of an incandescent light bulb? Does the light bulb produce visible
light? How can you tell?
2. Explain how the graph of a light bulb’s EM Radiation shows that X-rays are not produced.
3. In the spectrum made by the incandescent light bulb, what is the maximum wavelength produced and
how would you classify it?
Wavelength _______________________
Type: _____________________
4. Given your answer to #3, is an incandescent light bulb efficient at producing visible light? Explain and
suggest alternatives that could lower your electric bill and save your household money.
5. Based on the shape of the graph would you expect the light bulb to emit radio waves? Would the
amount be significant? Explain.
The BGR represents the Blue, Green and Red content of the light emitted by hot object.
6. What is the approximate color of a light bulb in the BGR indicator?
A. Yellow
B. Orange
C. White
D. Blue
Click Save. (The curve will turn yellow)
Part II Comparing spectra of different objects.
Set the temperature to 615 K, this is comparable to the temperature in a very hot oven. Notice that the
RED line shows the EM Radiation emitted (give off) by an oven. The line appears flat at the current
settings on the graph, so adjust the settings to be able to see the wavelength distribution. Zoom the y
axis in to read 0.001 and zoom the x-axis out to 24.
1. How is the shape of curve produced by an oven similar to the line produced by the light bulb?
2. How is the curve produced by the oven different from the curve produced by the light bulb?
3. What is the maximum wavelength produced by an oven and how would you classify it?
Wavelength _______________________
Type: _____________________
4. If the light goes out in your kitchen, could you see in the dark by the light emitted from the hot oven?
Explain.
Set the temperature to 5800K. This is approximately the surface temperature of the sun. You’ll need to
change the zoom on the vertical axis to 100 and the horizontal axis to 1.5.
5. Compare the maximum wavelength produced (the wavelength of the peak or top of the curve) made
by the light bulb to the most intense wavelength produced by the sun.
6. Describe the intensity and distribution EM radiation emitted (given off) by the sun and propose a
relationship between the maximum wavelength produced and the temperature of the glowing object.
7. Is there evidence of the sun producing harmful ultraviolet radiation? Explain.
The BGR represents the Blue, Green and Red content of the light emitted by hot object.
8. What is the approximate color of the sun using BGR?
A. Yellow
B. Orange
C. White
D. Blue
Part III The relationship between maximum wavelength and temperature.
Now you will record data and graph the relationship between maximum wavelength and temperature.
For the following temperatures determine the maximum wavelength emitted. Use the ruler tool to lineup the peak (top) of the curve to get an accurate reading from the x-axis.
Be sure to adjust and record your wavelength in nm!
Temperature (K)
Peak Wavelength (nm)
1/Wavelength (nm-1)
600 K
1200 K
2500 K
3500 K
4500 K
5500 K
Part IV Analysis of graphs and the slope of ‘Best Fit’ line:
1. Using Excel, Make a plot of Temperature (K) vs. Wavelength (nm). What is this kind of relationship
called?
2. Confirm this relationship by graphing Temperature (K) vs. 1/Wavelength (nm) and calculating the slope
of a best fit line. State a mathematical relationship between T and Peak Wavelength.
3. Write Wien’s Displacement Law, compare Wien’s constant to your slope and find your % error.
Part V Extension
Figure 3
In Figure 3 the temperature is adjusted for a peak emission in the yellow part of the spectrum. Note the
temperature is around 4620K for yellow and the BGR is light yellow.
1. Astronomers see red stars and blue stars but not green stars. Adjust the sliding temperature
adjustment for a peak wavelength of green and pick the approximate color you see in the BGR indicator?
You will probably need to adjust the zoom on each of the axes.
A. Yellow
B. Green
C. White
D. Blue
2. The temperature of stars in the universe varies with the type of star and the age of the star among
other things. By looking at the shape of the spectrum of light emitted by a star, we can tell something
about its average surface temperature.
i) If we observe a star's spectrum and find that the peak power occurs at the border between red
and infrared light, what is the approximate surface temperature of the star? (in kelvin)
ii) If we observe a star’s spectrum and find that the peak power occurs at the border between blue
and ultraviolet light, what is the surface temperature of the star? (in kelvin)