OPS - 4.4 Science in Action

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.

1050 K (1430 Fahrenheit)

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?

3000 K (4940 F)

Since we cannot physically collect data from stars and most other objects in the universe, almost all of the information we obtain from the universe comes from analyzing the light, or spectra, from those objects.The study of light is known as spectroscopy. As we have seen in this simulation, every blackbody emits light with an easily identified pattern known as the blackbody curve. This is the particular way the total light emitted by a blackbody varies with its frequency. The exact form of the curve depends only on the body's temperature. Since we can treat stars as blackbodies, this is incredibly useful in astronomy that shows us that the color of a star is also indicative of its temperature. Use the simulation to determine the surface temperature of the following star: Betelgeuse is a red supergiant star in the constellation Orion. Knowing that Betelgeuse has peak intensity in the red and infrared wavelengths, adjust the intensity scale and temperature until you can determine the approximate surface temperature of the star.

3500 K

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?

5800 K (9980 F)

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 500 and center the peak emission in the blue band. 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?

7000 K

Use Wien's Law to calculate the peak wavelength of Betelgeuse, based on the temperature found in Question #8.

828 nm

Based on the simulation, what type of light does the Sun produce the most?

Green visible light

What type of light does this light bulb produce most (i.e. at what wavelength does the spectrum have maximum intensity)?

Infrared light

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 0.8. 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. Even though the spectrum appears completely flat, objects at room temperature and below also emit their own light. If our eyes could detect infrared light, we would be able to see in the dark with warmer objects being brighter than others. In the introduction of this activity, we mentioned the temperature of your home on hot and cold days. Your body is kept warm in your home primarily by two ways: by direct contact with the air around you and by absorbing infrared light that is radiated from the walls. As you have seen in this activity, the light that is radiated from an object depends almost solely on the temperature of the object. Based on

The walls of the house are warmer during the summer. Therefore, they radiate more infrared light that can serve to warm our body.

In this equation: λ(max)= peak wavelength (cm) T = temperature (K) Based on what you have seen in the simulation and your knowledge of proportionality relationships learned this month, what is the relationship between temperature and peak wavelength?

They are inversely proportional.