11th Class Physics Thermal Properties of Matter / द्रव्य के तापीय गुण

  • question_answer 22)
    A body cools from \[{{80}^{o}}C\] to \[{{50}^{o}}C\] in 5 minutes. Calculate the time it takes to cool from \[{{60}^{o}}C\] to \[{{30}^{o}}C\]. The temperature of the surrounding is \[{{20}^{o}}C\].

    Answer:

    If T is the temperature of body and Ty is the temperature of surroundings, then according to Newton's law of cooling \[{{10}^{-3}}\] or \[=6\cdot 9\times {{10}^{7}}Pa;\] If the temperature of the body falls from \[=6\cdot 9\text{ }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{7}}}\text{ }\!\!\times\!\!\text{ }\left( \text{22/7} \right)\text{ }\!\!\times\!\!\text{ }{{\left( \text{3 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-3}}} \right)}^{\text{2}}}\]and \[\therefore \]in time t, then integrating the above relation, we have \[=4\left[ 6\cdot 9\text{ }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{7}}}\text{ }\!\!\times\!\!\text{ }\frac{\text{22}}{\text{7}}\text{ }\!\!\times\!\!\text{ 9 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-6}}} \right]=7\cdot 8\times \text{1}{{\text{0}}^{\text{3}}}\text{N}\] or \[1\cdot 1\times {{10}^{8}}Pa.\] or \[0\cdot 32{{m}^{3}}\]or \[=11\cdot 6\times {{10}^{11}}N{{m}^{-2}}\]or\[p=1\cdot 1\times {{10}^{8}}pa;\] or \[V=0\cdot 32{{m}^{3}};\] As per question condition (i), \[B=1\cdot 6\times {{10}^{11}}Pa\]\[\vartriangle V=\frac{\text{pV}}{\text{B}}=\frac{\left( 1\cdot 1\times {{10}^{8}} \right)\times 0\cdot 32}{1\cdot 6\times {{10}^{11}}}\]\[=2\cdot 2\times \text{1}{{\text{0}}^{\text{-4}}}{{\text{m}}^{\text{3}}}\]\[\because \]\[{{\text{S}}_{\text{LA}}}\text{,}{{\text{S}}_{\text{SA}}}\text{ and }{{\text{S}}_{\text{SL}}}\] \[\theta \] ..(2) As per question, condition (ii), \[{{\text{S}}_{\text{SL}}}\text{+}{{\text{S}}_{\text{LA}}}\text{cos }\!\!\theta\!\!\text{ =}{{\text{S}}_{\text{SA}}}\] \[\text{cos }\!\!\theta\!\!\text{ =}\frac{{{\text{S}}_{\text{SA}}}\text{-}{{\text{S}}_{\text{SL}}}}{{{\text{S}}_{\text{LA}}}}\].(3) Dividing (3) by (2), we get \[{{\text{S}}_{\text{SL}}}\text{}{{\text{S}}_{\text{SL}}}\text{,}\] \[\theta \] Ability is of the little account without opportunity.


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