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An Ideal Blackbody. A large cavity that has a very small hole and is maintained at a temperature T is a good approximation to an ideal radiator or blackbody.
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University Physics with Modern Physics, Books a la Carte Edition; Modified MasteringPhysics with Pearson eText -- ValuePack Access Card -- for ... eText -- Valuepack Access Card (14th Edition)
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- We can use Stefan-Boltzmann Law, P = o AeT“, to produce a very rough estimation of temperature of the Earth. Follow the steps below to estimate the temperature of the Earth. At the radius of the Earth's orbit (1 astronomical unit away from the Sun), the thermal radiation from the Sun has an intensity of about S = 1370 W/m², known as the "solar constant." a. In terms of solar constant S and radius of the Earth R, what is the total solar power (Pin) incident on and absorbed by the Earth? Assume that Earth can be treated like a blackbody and will absorb all radiation incident on it. Hint for (a) Pin Give your answer in terms of S, R, and other numerical constants (spell out Greek characters, i.e. "pi" for T). b. As the temperature of the Earth rises, the power emitted by the Earth (Pout) increases. Give an expression for power emitted by the Earth, in terms of its radius and other constants (see some of the constants used in Stefan-Boltzmann Law). Hint for (b) Pout Give your answer in…arrow_forwardA student is trying to decide what to wear.His bedroom is at 20°c.His skin Temperature is 35.0°c.The area of his exposed skin is 1.50 sq.mitres.People all over the world have skin that is dark in the infrared,with emessivity about 0.900.Find the net energy transfer from his body by radiation in 10.0 minutes.arrow_forwardAn incandescent lamp filament, with a surface area of 100mm^2, operates at a temperature of 2300 degrees Celsius. Assume that the filament acts like a blackbody(e = 1). (a) What is the rate of radiation from the filament? (b) If the walls of the room in which the lampoperates are at 27 degrees Celsius. What is the rate at which the filament absorbs radiation? (c) At what rate does electrical energy have to be supplied to the filament to keep its temperatureconstant? (Ignore conduction and convection losses from the filament.)arrow_forward
- Our sun is a standard sequence yellow dwarf star with a temperature of about 6000 K and a radius of about 7 x 10^8 m, emitting about 3.8 x 10^26 W. There are yellow giant stars with the same blackbody color (temperature) but with a radius 10 times larger than our sun (7 x 10^9 m). Estimate the power (emitted radiation) from one of these yellow giant stars.arrow_forwardThe Stefan-Boltzmann Law says that the light radiated from a perfect radiator ("blackbody") is proportional to the temperature raised to the fourth power: where σ is the Stefan-Boltzmann constrant (σ = 5.67 x 10-8 in MKS units) In equilibrium, F coming in equals F going out. At Mars' distance from the Sun, F coming in is 153 in MKS units. What is the blackbody temperature for Mars at a distance of 1.524 AU from the Sun?arrow_forwardA large cavity that has a very small hole and is maintained at a temperature T is a good approximation to an ideal radiator or blackbody. Radiation can pass into or out of the cavity only through the hole. The cavity is a perfect absorber, since any radiation incident on the hole becomes trapped inside the cavity. Such a cavity at 400 •C has a hole with area 6.00 mm2. How long does it take for the cavity to radiate 300 J of energy through the hole?arrow_forward
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