A question about Thermodynamic

優誌企業研究所

2013-03-09 9:05 pm

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Two metal blocks X and Y of the same mass and of initial termperatures 40 degree and 30 degree respectively are in good thermal contact as shown above.

The specific heat capacity of X is greater than that of Y. Assume no heat loss to the surrounding, why their temperature becomes the same and is higer than 35 degree when a steady state is reached?

回答 (1)

天同

2013-03-09 9:59 pm

✔ 最佳答案

Let m be the mass of X or Y, Cx and Cy be the specific heat capacities of X and Y respectively.

Hence, when they are in contact,
heat loss by X = heat gain by Y
i.e. m(Cx).(Tx) = m.(Cy).(Ty)
where Tx is the drop in temperature of X, and Ty is the rise in temperature of Y
thus, Tx/Ty = Cy/Cx

Because Cy < Cx
hence, Cy/Cx < 1
or Tx/Ty < 1
i.e. Tx < Ty

Therefore, the drop in temperature of X is less than the rise in temperature of Y. This only happens when the final temperature is above 35'C.

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