Physics Lab/ Radiation

Blackbody Radiation Lab 11 Go to http://phet. colorado. edu/simulations/sims. php? sim=Blackbody_Spectrum and click on Run Now. 1) In this lab, you will use the Blackbody Spectrum Simulation to investigate how the spectrum of electromagnetic radiation emitted by objects is affected by the object’s temperature. In this simulation, you can input the temperature and observe the spectrum of the radiation emitted. a) 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 degrees C) The temperature will be ~4000K which would be about 3276 degrees Celcius. ii) If we observe a stars 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 degrees C) The temperature would be about 7050 degrees Celcius. b) Light bulbs operate at 2500 degrees C. What is the wavelength at which the most power is emitted for a light bulb operating at 2500 C? The wavelength would be equal to 1000nm ii) Explain why regular incandescent bulbs waste a lot of energy. Be sure to include your reasoning. The majority of the light emitted is at wavelengths that are longer than that, that are visible. So the power going into the light bulb that is producing non-visible light is wasted. It is wasting energy that way, so regular incandescent bulbs are inefficient. ) In this problem we will explore the greenhouse effect by using the Greenhouse Effect Simulation available from http://phet. colorado. edu/simulations/sims. php? sim=The_Greenhouse_Effect a) Explore the simulation. True or False The only effect of increasing the number of clouds is to reduce the amount of sunlight absorbed by the surface of the earth. Clouds reduce the amount of sunlight absorbed by reflecting sunlight back away from earth. Clouds also can absorb infrared radiation emitted by the surface and then send it back to spae. True or False

Increasing the concentration of greenhouse gases, increases the amount of radiation that Earth emits to space. Earth used to emit the same amount of radiation it absorbed, but not now. So now the radiation that used to be absorbed by the earth is remitted down and absorbed by the ground. So the earth is taking in this radiation and is warming up. Without the damage and pollution humans have caused then this would not be the case and it would be in equilibrium. True or False When sunlight encounters a cloud, the cloud reflects about 10% of the sunlight back to space. The cloud reflects about 50% of the sunlight back to space. True or False

When there is a very large concentration of greenhouse gases, most of the IR radiation reaching space has interacted with greenhouse gas molecules on its way from the surface to space. Yes, the greenhouse gases absorb IR radiation. True or False The total amount of radiation absorbed by the Earth’s surface is not affected by the concentration of greenhouse gases in the atmosphere. Sunlight and greenhouse gases are absorbed by earth. When earths atmosphere has greenhouse gases the IR radiation is emitted by the surface and absorbed and also redirected back down to the surface. So the total amount of radiation absorbed is increasing.

True or False At higher temperatures, the Earth’s surface emits more IR radiation. Yes because if the temperature increases then the power radiated increases as well. True or False During the ice age, the amount of sunlight absorbed by the Earth’s surface decreased. During the ice age the ice on the earth would also reflect sunlight back, making less sunlight absorbed by the earths surface. True or False All greenhouse gases are from anthropogenic sources (that is due to man’s activities). Not true, most are naturally occurring but man has increased greenhouse gasses especially the high amounts of carbon dioxide present now…from man’s doing.