Thermal Properties of Matter

JEE Main level, numerical answer, medium

98 of 126

Question 98 of 126

A rod CDCD of thermal resistance 10.0KW−110.0{KW}^{-1} is joined at the middle of an identical rod ABAB as shown in figure. The ends A,BA,B and DD are maintained at 200∘C,100∘C200^{\circ}C,100^{\circ}C and 125∘C125^{\circ}C respectively. The heat current in CDCD is PWPW. The value of PP is

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Answer: 2

QAC+QDC=QCB{Q}_{AC}+{Q}_{DC}={Q}_{CB}
KA(200−t)ℓ2+KA(125−t)ℓ=(t−100)KAℓ2\dfrac{KA(200-t)}{\dfrac{\ell }{2}}+\dfrac{KA(125-t)}{\ell }=\dfrac{(t-100)KA}{\dfrac{\ell }{2}}
400−2t+125−t=2t−200400-2t+125-t=2t-200
725=5t725=5t
t=145ºCt=145ºC
QCD=KA(145−125)ℓ=20ℓKA=2W{Q}_{CD}=\dfrac{KA(145-125)}{\ell }=\dfrac{20}{\dfrac{\ell }{KA}}=2W

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