JCECE Engineering JCECE Engineering Solved Paper-2013

  • question_answer
    The resistance of a resistance thermometer have values \[2.71\] and \[3.70\] ohms at \[{{10}^{o}}C\] and \[{{100}^{o}}C\] respectively. The temperature at which the resistance is \[3.26\,\,ohm\] is

    A) \[{{40}^{o}}C\]                 

    B) \[{{50}^{o}}C\]

    C)  \[{{60}^{o}}C\]                

    D)  \[{{70}^{o}}C\]

    Correct Answer: C

    Solution :

    We have,                 \[{{R}_{t}}={{R}_{0}}(1+\alpha t)\] Here\[,\]             \[3.70=2.71[1+\alpha (100-10)]\]              ? (i) and        \[3.26=2.71[1+\alpha (x-10)]\]   ... (ii) From Eqs. (i) and (ii)                 \[\alpha =\frac{3.70-2.71}{90\times 2.71}\approx \frac{1}{90}\times 2.71\]           ? (iii) Substituting Eq. (iii) in Eq. (i)                 \[3.26=2.71\left[ 1+\frac{1}{90\times 2.71}\times (x-10) \right]\]                         \[=2.71+\frac{x-10}{90}\] or            \[\frac{x-10}{90}=3.26-2.71=0.55\] \[\Rightarrow \]               \[x=(90\times 0.55)+10\]                    \[=49.5+10={{59.5}^{o}}C\]                    \[\approx {{60}^{o}}C\]


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