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The emissivity of tungsten is aproximate...

The emissivity of tungsten is aproximately 0.35. A tungsten sphere 1 cm in radius is suspended within a large evacuated enclosure whose walls are at 300 K. What power input is required to maintain the sphere at a temperature of 3000 K if heat conduction along the support is neglected?`sigma=5.67xx10^-8` SI units.

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Net heat lost by sphere per second`H_("net")=esigmaA(T^4-T_0^4)`
where `T=` temperature of sphere`=3000K`
`T_0=` temperature of surrounding `=300KimpliesA=4pir^2=4pi(0.01)^2`
To maintain constant temperature, power input required`=`net `P_("input")=esigmaA(T^4-T_0^4)`
`P_("input")=0.35xx5.67xx10^-8xx4p(0.01)^2xx(3000^4-300^4)=2019.8W`
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