#### Question

A pinhole is made in a hollow sphere of radius 5 cm whose inner wall is at temperature 727^{o}C. Find the power radiated per unit area. [Stefan’s constant σ = 5.7 x 10^{-8} J/m^{2} s K4 , emissivity (e) = 0.2]

#### Solution

Given:-

T = 727 + 273 = 1000 K,

σ = 5.7 x 10^{-8} J/m^{2}sK^{4}, e = 0.2

To find:- Power radiated (E)

Formula:-

`(E)Q/(At)=sigmaeT^4`

Calculation:- From formula,

E = 0.2 x 5.7 x 10^{-8} x (1000)^{4}

^{ = 11400}

**∴ **E = 1.14 x 10^{4} watt/m^{2}

The power radiated per unit area is 1.14 x 10^{4} watt/m^{2}.

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Solution A Pinhole is Made in a Hollow Sphere of Radius 5 Cm Whose Inner Wall is at Temperature 727 C. Find the Power Radiated per Unit Area. Concept: Temperature and Heat.