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Manipal Medical Manipal Medical Solved Paper-2005

  • question_answer
    A body at a temperature of\[728{}^\circ C\]and has surface area 5 cm, radiates 300 J of energy each minute. The emissivity is: (Given: Boltzmann constant\[=5.67\times {{10}^{-8}}\]watt\[{{m}^{2}}{{K}^{4}}\])

    A)  \[e=0.18\]        

    B)  \[e=0.02\]

    C)  \[e=0.2\]        

    D)  \[e=0.15\]

    Correct Answer: A

    Solution :

     \[Q=EAt=e\sigma ({{T}^{4}}-T_{0}^{4})\]At where\[t=\]time \[{{T}_{0}}=\]temperature of surrounding When, \[T>{{T}_{0}}\] \[Q=e\sigma {{T}^{4}}\]At \[300=e(5.67\times {{10}^{-8}}){{(1000)}^{4}}(5.00\times {{10}^{-4}})(60)\] \[e=0.18\]


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