A spherical body of radius b=4πm has a concentric cavity of radius a=2πm as shown. Thermal conductivity of the material is 100W/m∘C. Find the thermal resistance between inner and outer surface.
A
6.25×10−4∘C/W
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B
1.25×10−4∘C/W
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C
6.5×10−4∘C/W
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D
3.75×10−4∘C/W
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Solution
The correct option is A6.25×10−4∘C/W Given, Outer radius of spherical body (b)=4πm Inner radius of spherical body (a)=2πm Thermal conductivity of material (k)=100W/m∘C Then, thermal resistance (R)=14πk(1a−1b) =14π×100(π2−π4) =11600=6.25×10−4∘C/W