JEE Main & Advanced Physics Transmission of Heat Question Bank Conduction

  • question_answer
    The coefficients of thermal conductivity of copper, mercury and glass are respectively Kc, Km and Kg such that Kc > Km > Kg. If the same quantity of heat is to  flow per second per unit area of each and corresponding temperature gradients are Xc, Xm and Xg, then                                            [MP PMT 1990]

    A)            \[{{X}_{c}}={{X}_{m}}={{X}_{g}}\]                                   

    B)            \[{{X}_{c}}>{{X}_{m}}>{{X}_{g}}\]

    C)            \[{{X}_{c}}<{{X}_{m}}<{{X}_{g}}\]                                   

    D)            \[{{X}_{m}}<{{X}_{c}}<{{X}_{g}}\]

    Correct Answer: C

    Solution :

                       \[\frac{Q}{At}=K\frac{\Delta \theta }{l}\]Þ \[K\frac{\Delta \theta }{l}\]= constant Þ \[\frac{\Delta \theta }{l}\propto \frac{1}{K}\] Hence  If \[{{K}_{c}}>{{K}_{m}}>{{K}_{g}}\], then            \[{{\left( \frac{\Delta \theta }{l} \right)}_{c}}<{{\left( \frac{\Delta \theta }{l} \right)}_{m}}<{{\left( \frac{\Delta \theta }{l} \right)}_{g}}\Rightarrow {{X}_{c}}<{{X}_{m}}<{{X}_{g}}\] because higher K implies lower value of the temperature gradient.


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