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NEET Sample Paper NEET Sample Test Paper-78

  • question_answer
    The thermo emf-E in volts of a certain thermocouple is found to vary with temperature difference \[\theta \] in \[{}^\circ C\] between the two junctions according to the relation \[E= 30 \theta \,\,- \frac{{{\theta }^{2}}}{15}\] then the neutral temperature of thermocouple is                                                        

    A)  \[400{}^\circ C\]                     

    B)  \[225{}^\circ C\]

    C)  \[450{}^\circ C\]                     

    D)  \[30{}^\circ C\]

    Correct Answer: B

    Solution :

    As, \[\operatorname{E}=30\,\,\theta -\frac{{{\theta }^{2}}}{15}\] For neutral temperature, \[\frac{dE}{d\theta }=0\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\frac{dE}{d\theta }=30-\frac{2\,\,\theta }{15}=0\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,30=\frac{2\,\theta }{15}\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\theta =\frac{15\times 30}{2}\,\,=\,\,225{}^\circ C\]


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