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The emissivity of tungsten is 0.4. A tun...

The emissivity of tungsten is 0.4. A tungsten sphere with a radius of 4.0 cm 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 supports is neglected ?
Take, `sigma = 5.67 xx (10^-8) Wm^2-K^4`.

Text Solution

Verified by Experts

The correct Answer is:
A, C, D
`P = e_rsigmaA (T^4 - T_(0)^4)`
`(0.4)(5.67 xx 10^-8)(4pi)(4 xx 10^-2)^2 [(3000)^4`
`-(300)^4]`
`= 3.7 xx (10^4)W`
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