JEE Main & Advanced Physics Transmission of Heat Question Bank Critical Thinking

  • question_answer
    A black metal foil is warmed by radiation from a small sphere at temperature T and at a distance \[d\]. It is found that the power received by the foil is `P'. If both the temperature and the distance are doubled, the power received by the foil will be                                                             [MP PMT 1997]

    A)            16P

    B)            4P

    C)            2P  

    D)            P

    Correct Answer: B

    Solution :

                       Energy received per second i.e., power \[P\propto ({{T}^{4}}-T_{0}^{4})\]                    Þ \[P\propto {{T}^{4}}\] \[(\because \,{{T}_{0}}<<T)\]                    Also energy received per sec (p)\[\propto \frac{1}{{{d}^{2}}}\]                    (inverse square law)                    Þ \[P\propto \frac{{{T}^{4}}}{{{d}^{2}}}\] Þ \[\frac{{{P}_{1}}}{{{P}_{2}}}={{\left( \frac{{{T}_{1}}}{{{T}_{2}}} \right)}^{4}}\times {{\left( \frac{{{d}_{2}}}{{{d}_{1}}} \right)}^{2}}\]            Þ \[\frac{P}{{{P}_{2}}}={{\left( \frac{T}{2T} \right)}^{2}}\times {{\left( \frac{2d}{d} \right)}^{2}}=\frac{1}{4}\] Þ\[{{P}_{2}}=4P.\]


You need to login to perform this action.
You will be redirected in 3 sec spinner