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如右图，体积为V、内壁光滑的圆柱形导热气缸顶部有一质量和厚度均可忽略的活塞；气缸内密封有温度为2.4T0、压强为1.2P0的理想气体．P0和T0分别为大气的压强和温度．已知：气体内能U与温度T的关系为U=aT，a为正的常量；容器内气体的温度缓慢降低的过程中，最后气体的压强变为P0和T0．热力学第一定律为△U=W+Q．求：

（1）气缸内气体的体积V1：

（2）在活塞下降过程中，气缸内气体放出的热量Q．

答案

（1）在气体由压缩P=1.2P0到P0时，V不变，温度由2.4T0变为T1，由查理定律得

T1
T
=
P0
P
…①

在气体温度由T1变为T0的过程中，体积由V减小到V1，气体压强不变，由着盖•吕萨克定律得

V
V1
=
T1
T0
…②

由①②式得 V1=0.5V…③

（2）活塞下降过程中，活塞对气体的功为W=P0（V-V1）

在这一过程中，气体内能的减少为△U=a（T1-T0）

由热力学第一定律得，气缸内气体放出的热量为Q=W+△U

得出：Q=

1
2
P0V+aT0

答：（1）气缸内气体的体积为0.5V：

（2）在活塞下降过程中，气缸内气体放出的热量为

1
2
P0V+aT0．

单项选择题

(四)


"Congratulations, Mr. Jones, it’s a girl. "
Fatherhood is going to have a different meaning and bring forth a different answer from every man who hears these words. Some feel proud when they receive the news, while others worry, wondering whether they will be good fathers. Although there are some men who like children and may have had considerable experience with them, others do not particularly care for children and spend little time with them. Many fathers and mothers have been planning and looking forward to children for some time. For other couples, pregnancy was an accident that both husband and wife have accepted willingly or unwillingly.
Whatever the reaction to the birth of a child, it is obvious that the change from the role of husband to that of father is a difficult task. Yet, unfortunately, few attempts have been made to educate fathers in this re-socialization process. Although many good books have been written about American mothers, only recently have some books discussed the role of a father.
It is argued by some writers that the transition to the father’s role, although difficult, is not nearly as great as the transition the wife must make to the mother’s role. The mother’s role seems to require a complete transformation of daily routine and adaptation to a new life, on the other hand, the father’s role is less demanding and immediate. However, even though we have mentioned the fact that growing numbers of women are working outside the homey the father is still thought by many as the breadwinner in the household.

It is stated in the passage that ______.

A．some parents are not prepared to have a child

B．young couples do not like children at all

C．working couples do not have much time to take care of their children

D．many parents look forward to having a boy as their first child
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