Blackbody spectrum sim homework answers

1. Introduction Choose One • 10 points It is mentioned in the week 4 course notes that the understanding of something called blackbody radiation lead to the formulation of quantum mechanics. This first part of your Physical Science in Action this week will take a brief look at this phenomenon. As a reminder, here is a picture of the electromagnetic spectrum. It is oriented in the same direction as the spectrum you will use in today's simulation. Have you ever noticed that on a cool winter day that your house feels much cooler than on a warm summer day even though your thermostat is set to the same temperature? You are probably also aware that as objects heat up they will begin to give off visible light and also change color as they get hotter. For example a piece of metal placed in a furnace will begin to glow deep red, then orange, and then become “white hot”. Why do you think this is? Both of these questions will be easily answered by learning about blackbody radiation. Open the following link: http://phet.colorado.edu/sims/blackbody-spectrum/blackbody-spectrum_en.html It just so happens that regardless of the material, when objects are heated up they will start to glow and change colors at near identical temperatures. The plot that you see is called a blackbody spectrum. This plot tells us the intensity or the “amount” of light that an object will emit at different wavelengths (or “colors”). The visible wavelengths are marked by their colors on the plot. To the right of the visible band is lower energy infrared light. To the left of this band is higher energy ultraviolet (UV) light. Click the + button that is to the left of the intensity scale (far left side of the screen) such that the top of the scale is at .001. (in the picture above the top of the scale says 100). Now use the temperature slider to the right, and take the temperature all the way down to 300 Kelvin (80 Fahrenheit). Now slowly begin to raise the temperature. At approximately what temperature would a heated material (metal, wood, etc.) begin to give off visible light at a deep red color? Note: This will be the temperature where your spectrum first begins to come off of the wavelength axis in the visible region, and so is giving off a small amount of red light. • • • • 2 500 K (440 Fahrenheit) 1050 K (1430 Fahrenheit) 1800 K (2780 Fahrenheit) 2500 K (4040 Fahrenheit) 2. Blackbody Spectrum Choose One • 10 points Click the - button that is to the left of the intensity scale to zoom out such that the top of the scale is at 10. Move the temperature slider to that of a light bulb. The red part of the thermometer on the far right should just be touching the line marked light bulb. At approximately what temperature does the filament in a household light bulb operate? Note: This is written in blue in the simulation. • • • • 660 K (728 F) 1800 K (2780 F) 3000 K (4940 F) 5700 K (9800 F) 3. Blackbody Spectrum Choose One • 10 points What type of light does this light bulb produce most (i.e. at what wavelength does the spectrum have maximum intensity)? • • • • Infrared light Red visible light Violet visible light Ultraviolet light 4. Blackbody Spectrum Choose One • 10 points Click the - button that is to the left of the intensity scale to zoom out such that the top of the scale is at 100. Move the temperature slider to that of the Sun. The red part of the thermometer on the far right should just be touching the line marked Sun. Approximately what temperature is the surface of the Sun? • • • • 2100 K (3320 F) 4500 K (7640 F) 5700 K (9800 F) 9800 K (17,180 F) 5. Blackbody Spectrum Choose One • 10 points Based on the simulation, what type of light does the Sun produce the most? • 3 Infrared light • • • Green visible light Orange visible light Ultraviolet light 6. Blackbody Spectrum Choose One • 10 points Relative to the peak intensity in the Sun’s spectrum, the Sun emits nearly equal amounts of light across the entire visible part of the EM-spectrum. This is demonstrated by the star shaped symbol at the top of the simulation being white. Therefore, if you look at the Sun when it is directly overhead on a clear day, it will appear white. Click the - button that is to the left of the intensity scale to zoom out such that the top of the scale is at 316. Use the star shaped symbol above your graph and to the right of the blue, green, and red dots to estimate the temperature at which something will begin to glow blue. At approximately what temperature does the object gain a faint blue tint? Note: This will also be the temperature where the max intensity of the objects spectrum is in the blue portion of the visible spectrum. • • • • 3000 K (4940 F) 6600 K (11,420 F) 7900 K (13,760 F) Object cannot glow blue at any temperature. 7. Blackbody Spectrum Choose One • 10 points Note that in the above question, although the object still emits all colors of visible light, it appears blue now instead of white because of the significant difference in the intensity or amount of blue light radiated versus the amount of red light emitted. Click the + button that is to the left of the intensity scale to zoom in such that the top of the scale is at 1. Now slowly decrease the temperature from 5000K down to 300K (room temperature). Notice how the entire spectrum decreases in intensity and moves to the right into the infrared region.