Helen's+Lab+Notebook

=Blackbody Radiation Lab. 1= toc September 14, 2010

Part 1: Light, Waves, Wavelengths, and Frequency
1. What is wavenumber? Wavenumber is the number of cycles per centimeter of length.

2. Why is wavenumber preferred by scientists who discuss IR light? It is preferred by scientists because when IR light is described by the wavenumber, it is a nice and easy to remember number.

3. What is the period (T) of IR radiation (wavelength around 10 micrometers)? 10 micrometers = 0.001 centimeters 3e10 cm/s / 0.001 cm = 3e13 cycles per second 1 / 3e13 cycles per second = 3.3e-14 seconds per cycle

4. Infrared light has a wavelength of about 10 microns. What is its wavenumber in cm-1? 10 microns = 0.001 centimeters 1 / 0.001 cm = 1000 cycles per centimeter

5. Visible light has a wavelength of about 0.5 microns. Whas is its frequency in Hz (cycles per second)? 0.5 microns = 5.0e-5 centimeters 3e10 cm/s / 5.0e-5 cm = 6e14 cycles per second

Part 2: Blackbody Spectrum - a link between wavelength and heat
1. Notice the units that wavelength are shown in -- nanometers. Sometimes wavelengths are reported in micrometers, sometimes in centimeters and sometimes even in meters. Explain when and why it might be more convenient to use units of nanometers and when it might be convenient to use units of meters. The unit is whichever one that would describe the wavelength most accurately in a straightforward way.

2. As temperature is decreased from the highest possible temperature on this stimulation, describe what happens to the peak wavelength of light emitted by a blackbody? As temperature is decreased on this stimulation, the peak wavelength of the light increases.

3. Which is hotter, a blackbody emitting radiation in the visible light range of wavelengths or a blackbody emitting in the infrared range of wavelengths? Explain your answer based on the information you gathered in Parts I & II. A blackbody emitting radiation in the visible light range would be hotter since infrared light has longer wavelengths which mean that the temperature is lower.

Part 3: Comparing Sun and Earth Shine
1. It is very similar to the non-interactive figure above but there are some key differences. Leave out the line labeled " lSubscript[, max]" and the interactivity of this figure as compared to the one above. What are the main differences between the two figures? The main difference is the shape of the graph. In the figure form part 2, the peak wavelength shifts from left to right as the temperature changes. But in the figure from part 3, the maximum wavelength increases vertically as the temperature increases.

2. Set the slider bar on the figure below to a temperature of 3500 K. What type of electromagnetic radiation would you expect to find in the range of the emissions of this spectrum (length units on the y-axis may need some conversion and thought)? What is the peak irradiance? The peak wavelength is around 800 nanometers so I would expect infrared radiation. 3. Now set the temperature to 5100 K. What type of electromagnetic radiation would you expect find in the range of the peak emission of this spectrum? What is the peak irradiance? The peak wavelength is around 570 nanometers so I would expect visible light radiation.

4. Explain the differences in the shapes of the spectra at these two temperatues. At the lower temperature, the slopes of the spectra is much steeper, and the peak wavelength is much higher.

Part 4: Greenhouse Gas and Earth Shine
1) Use the image below to describe how this would work with a closed up car parked in a sunny spot on cool day. Put in labels where they are need to show the different types of radiation and what happens to it. How good an analogy do think this is for the Greenhouse Effect on Earth? Explain.

While some of the sunlight radiation (IR, UV,etc) gets reflected by the car indicated by the red line, other radiation passes through and heats up the car inside. Thus, the car becomes a blackbody and as the temperature increases, the car itself begins to radiate heat indicated by the small arrows pointing upward. This is a good analogy for the Greenhouse effect on Earth because like the car, the Earth is a blackbody and emits radtiation. In addition, the car body itself acts like the greenhouse gases in the atmosphere trapping the radiation and heat inside.