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AIIMS AIIMS Solved Paper-2014

  • question_answer
    A body at a temperature of\[728{}^\circ C\]and has surface area\[5\text{ }c{{m}^{2}}\]radiates 300 J of energy each minute. The emissivity is (Given Boltzmann constant\[=\text{5}.\text{67}\times \text{1}{{\text{0}}^{-\text{8}}}\text{W}{{\text{m}}^{\text{2}}}{{\text{K}}^{\text{4}}})\]

    A) \[e=0.18\]

    B) \[e=0.02\]

    C) \[e=0.2\]                            

    D) \[e=0.15\]

    Correct Answer: A

    Solution :

                    \[a=E\,\,\,At=e\sigma ({{T}^{4}}-T_{0}^{4})At\] where, t = time \[T_{0}^{{}}\] = temperature of surrounding when\[T>{{T}_{0}}\,,\,\,Q=e\sigma {{T}^{4}}At\] \[300=e\times (5.67\times {{10}^{-8}}){{(1000)}^{4}}(5.00\times {{10}^{-4}})\] \[\text{e }=0.\text{18}\]                                


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