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BHU PMT BHU PMT (Screening) Solved Paper-2009

  • question_answer
    The tungsten filament of an electric lamp has a surface area A and a power rating P. If the emissivity of the filament is\[\varepsilon \]and\[\sigma \]is Stefan's constant, the steady temperature of the tungsten will be

    A)  \[T={{\left( \frac{P}{A\varepsilon \sigma } \right)}^{4}}\]            

    B)  \[T=\left( \frac{P}{A\varepsilon \sigma } \right)\]

    C)   \[T={{\left( \frac{A\varepsilon \sigma }{P} \right)}^{\frac{1}{4}}}\]         

    D)   \[T={{\left( \frac{P}{A\varepsilon \sigma } \right)}^{\frac{1}{4}}}\]

    Correct Answer: D

    Solution :

                     Radiant power P is denned as energy radiated per unit area. ie,           \[P=\frac{Q}{t}=A\varepsilon \sigma {{T}^{4}}\] \[\Rightarrow \]               \[T={{\left( \frac{P}{A\varepsilon \sigma } \right)}^{1/4}}\]


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