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# A Spherical Tungsten Piece of Radius 1.0 Cm is Suspended in an Evacuated Chamber Maintained at 300 K. the Piece is Maintained at 1000 K by Heating It - Physics

ConceptStefan's Law

#### Question

A spherical tungsten piece of radius 1.0 cm is suspended in an evacuated chamber maintained at 300 K. The piece is maintained at 1000 K by heating it electrically. Find the rate at which the electrical energy must be supplied. The emissivity of tungsten is 0.30 and the Stefan constant σ is 6.0 × 10−8 W m−2 K−4.

#### Solution

Given:

Radius of the spherical tungsten, r = 10−2 m

Emissivity of the tungsten, e = 0.3

Stefan's constant, σ = 6.0 × 10−8 W m−2 K−4

Surface area of the spherical tungsten, A = 4πr2

A = 4 π (10−2)2

A = 4 π × 10−4 m2

Rate at which energy must be supplied is given by

eσA (T24 - T14)

= (0.3)× 6 × 10-8 × 4π × 10-4×((1000)4 - (300)4)

= 22.42 ≈ watt = 22 watt

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Solution A Spherical Tungsten Piece of Radius 1.0 Cm is Suspended in an Evacuated Chamber Maintained at 300 K. the Piece is Maintained at 1000 K by Heating It Concept: Stefan's Law.
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