During periods of high activity, the Sun has more sunspots than usual. Sunspots are cooler than the rest of the luminous layer of the Sun’s atmosphere (the photosphere). Paradoxically, the total power output of the active Sun is not lower than average but is the same or slightly higher than average. Work out the details of the following crude model of this phenomenon. Consider a patch of the photosphere with an area of 5.10 × 1014 m2. Its emissivity is 0.965. a) Find the power it radiates if its temperature is uniformly 5800oK, corresponding to the quiet Sun. b) To represent a sunspot, assume 10.0% of the patch area is at 4800oK and the other 90.0% is at 5890oK. Find the power output of the patch.

During periods of high activity, the Sun has more sunspots than usual. Sunspots are cooler than the rest of the luminous layer of the Sun’s atmosphere (the photosphere). Paradoxically, the total power output of the active Sun is not lower than average but is the same or slightly higher than average. Work out the details of the following crude model of this phenomenon. Consider a patch of the photosphere with an area of 5.10 × 1014 m2. Its emissivity is 0.965. a) Find the power it radiates if its temperature is uniformly 5800oK, corresponding to the quiet Sun. b) To represent a sunspot, assume 10.0% of the patch area is at 4800oK and the other 90.0% is at 5890oK. Find the power output of the patch.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter11: Heat Transfer By Radiation

Section: Chapter Questions

Problem 11.48P

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