AP Physics Name:________________ Blackbody Lab ! Website for virtual lab http://phet.colorado.edu/sims/blackbody-spectrum/blackbody-spectrum_en.html ! Background: A “blackbody” is a term used to describe the light given by an object that only gives off emitted light, in other words it doesn’t reflect light. Of course in order for such an object to emit light it must get hot. In this lab you are going to observe the nature of light given off by hot objects and determine if there is an empirical relationship between an object’s temperature and the light emitted. ! Part I Characteristics of the blackbody spectrum of an incandescent light bulb. ! Set the temperature of the blackbody to 3000 K. This is approximately the temperature of the tungsten filament in an incandescent light bulb which is a good black body. Use the zoom tools so that you can observe a large peak (3.16 on the vertical axis and 3 on the horizontal axis would be good. Be clear about the information on each axis. Intensity is the amount of light given off and the wavelength of light is given on the horizontal axis. ! 1. Based on the graph, does the light bulb produce visible light? How can you tell? !! 2. Does the light bulb produce X-rays? How can you tell? !! 3. In the spectrum made by the light bulb, which wavelength is most intense and how would you classify it? ! Wavelength _______________________ Type:_____________________ ! 4. Given your answer to #3 is an incandescent light bulb very good for it’s intended use? Explain and suggest
alternatives. !!! 5. Based on the shape of the graph would you expect the light bulb to emit radio waves? Would the amount be
significant? Explain. !!! 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 is the radiation emitted by the oven. The line should appear flat, but it isn’t. Zoom the y axis in to read . 001 and zoom the x-axis out. !
1. How is the curve produced by the 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. If the power goes out in your kitchen, could you see in the dark using light from hot oven? Explain. !! Set the temperature to 5600K. This is approximately the surface temperature of the sun. You’ll need to zoom in on the horizontal axis and zoom out on the vertical axis. ! 4. Compared the most intense wavelength produced by the light bulb to the most intense produced by the sun. !! 5. Explain the relationship you see between the radiation emitted by the sun and the visible spectrum. !!! 6. Is there evidence of the sun producing harmful ultraviolet radiation? Explain. !!! Part III The relationship between peak wavelength and temperature. ! Now you will explore the relationship between peak wavelength and temperature. For the following temperatures determine the peak wavelength using the ruler tool to help you line-up the peak with the x-axis. Be careful to make sure your wavelength is in nm! ! Temperature (K) Peak Wavelength (nm!)
! 600 K
! 1200 K
! 2500 K
! 3500 K
! 4500 K
Analysis ! 1. Make a plot of Temperature (K) vs Wavelength (nm). What relationship do you see? !!!!!!!!! 2. Confirm the inverse relationship by graphing Temperature (K) vs 1/ Wavelength (nm). Record the slope of your line and state the mathematical relationship between T and Peak Wavelength. !!!! 3. Look up Wien’s Displacement Law and compare to your findings in terms of a % error.
! 5500 K