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The Earth receives solar energy at 8.2 J cm⁻² min⁻¹. Treating the Sun as a black body and given that it subtends an angle of 0.53 deg at the Earth, estimate the Sun's surface temperature. (Stefan constant sigma = 5.67 x 10⁻⁸ W m⁻² K⁻⁴.)

1. about 5800 K
2. about 3200 K
3. about 8400 K
4. about 11600 K

Correct answer: about 5800 K

Solution

Converting and solving S = sigma*T⁴*(theta/2)² gives T close to 5800 K, the Sun's effective surface temperature.

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