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A metal ball with surface area 200 cm² is at 527 degC and is placed inside an enclosure kept at 27 degC. If the emissivity of the ball's surface is 0.4, find the net rate at which the ball loses heat. (Stefan constant sigma = 5.67 x 10⁻⁸ J/m²-s-K⁴.)

1. 108 joules approx
2. 168 joules approx
3. 182 joules approx
4. 192 joules approx

Correct answer: 182 joules approx

Solution

P = e*sigma*A*(T⁴ - T0⁴) = 0.4*5.67e-8*0.02*(800⁴ - 300⁴) approx 182 W (J/s).

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