一定质量的理想气体的状态变化过程如图中直线段AB所示，C是AB的_爱下问搜题

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问题多选题

一定质量的理想气体的状态变化过程如图中直线段AB所示，C是AB的中点，则（　　）

A．从状态A变化到状态B的过程中，气体的内能保持不变

B．从状态A变化到状态B的过程巾，气体的温度先升高后降低

C．从状态A变化到状态C，气体一定吸热

D．从状态A变化到状态B的整个过程，气体一定吸热

答案

根据理想气体状态方程：

PV

T

=C（常数）

解得：P=T

1

V

所以图象中的等温线是在第一象限的双曲线的一支．越向上温度越高，AB两点在同一条等温线上．所以从A到B到C的过程中，温度先升高，后降低，故B正确．

因为温度是气体内能的标志，温度越高内能越大，所以整个过程内能先增大，后减小，故A错误．

根据热力学第一定律：△U=W+Q，全过程体积增大气体对外做功，W为负值，初末状态温度相同，△U=0，所以Q必须为正数，即气体一定要吸热，故C正确．

根据热力学第一定律：△U=W+Q，A到B过程中体积增大气体对外做功，W为负值，温度升高，△U大于零，所以Q必须为正数，即气体一定要吸热，故D正确．

故选：BCD

单项选择题

Advertisers tend to think big and perhaps this is why they’re always coming in for criticism. Their critics seem to resent them because they have a flair for self-promotion and because they have so much money to threw around. "It’s iniquitous," they say, "that this entirely unproductive industry (if we can call it that) should absorb millions of pounds each year. It only goes to show how much profit the big companies arc making. Why don’t they stop advertising and reduce the price of their goods After all, it’s the consumer who pays."
The poor old consumer. He would have to pay a great deal more if advertising didn’t create mass markets for products. It is just because of the heavy advertising that consumer goods are so cheap. But we get the wrong idea if we think the only purpose of advertising is to sell goods. Another equally important function is to inform. A great deal of the knowledge we have about household goods derives large from the advertisements we read. Advertisements introduce us to new products or remind us of the existence of ones we already know about. Supposing you wanted to buy a washing-machine, it is more than likely you would obtain details regarding performance, price, etc. from an advertisement.
Lots of people pretend that they never read advertisements, but this claim may be seriously doubted. It is hardly possible not to read advertisements these days. And what fun they often are, too] Just think what a railway station or a newspaper would be like without advertisements. Would you enjoy gazing at a blank wall or reading railway by-laws while waiting for a train Would you like to read only closely-printed columns of news in your daily paper A cheerful, witty advertisement makes such a difference to a drab wall or a newspaper full of the daily ration of calamities.
We must not forget, either, that advertising makes a positive contribution to our pockets. Newspapers, commercial radio and television companies could not subsist without this source of revenue. The fact that we pay so little for our daily paper, or can enjoy so many broadcast programs is due entirely to the money spent by advertisers. Just think what a newspaper would cost if we had to pay its full price !
Another thing we shouldn’t forget is the "little ads", which are in virtually every newspaper and magazine. What a tremendously useful service they perform for the community ! Just about anything can be accomplished through these columns. For example, you can find a job, buy or sell a house, announce a birth, marriage or death in what used to be called the "hatch, match and dispatch" columns; but by far the most fascinating section is the personal or "agony" column. No other item in a newspaper provides such entertaining reading or offers such a deep insight into human nature. It’s the best advertisement for advertising there is!

The word "drab" (Paragraph 3) might mean______

A. impressive.
B. nonconformist.
C. insightful.
D. unappealing.

名词解释

农业资源。