SSC JE Mechanical Engineering 2017 Set 1 Paper

Question : 109 of 200

Marks: +1, -0

Which surface will have the least emissivity ?

Smooth glass
Plaster
Aluminium foil
Concrete

Solution:

Emissivity is the value given to materials based on the ratio of heat emitted compared to a perfect blackbody, on a scale from zero to one. A blackbody would have an emissivity of 1 and a perfect reflector would have a value of 0.

\table \Materials \surface, \Thermal \emissivity;\Aluminium \foil ,0.03;\Plaster{, }\rough, 0.89;\Concrete{, }\rough, 0.91;\Glass{, } \smooth ,0.91

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