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我国首条同塔双回路100万伏特高压交流输电工程--“皖电东送”工程，即利用淮南丰富的煤炭资源，变输煤为输电，使淮南成为华东地区的能源基地．工程西起安徽淮南，经皖南、浙北到达上海，线路全长656公里，整个工程计划2013年底建成投运．

（1）工程建成后，淮南火力发电厂每年能向华东地区输送超过500亿度电，如果这些电能全部通过燃烧煤炭来生产完成，那么一年至少要消耗多少吨煤炭？（煤的热值为3×107J/kg）

（2）和一般高压输电线路相比，特高压具有输送容量大，输送距离远，电能损耗低等优点．假设甲、乙两地间的一条输电线的电阻是20欧，那么用200千伏的高压输送电能的功率为6×105千瓦，这条输电线损耗的电功率是多少千瓦？如果改用1000千伏的特高压输电，那么这条导线上损耗的电功率会减少多少千瓦？

答案

（1）根据题意可得，消耗煤炭产生的热量：

Q=500亿kW•h=500×109×3.6×06J=1.8×1018J，

∵Q=mq，

∴消耗的煤炭：

m=

Q
q
=
1.8×1018J
3×107J/kg
=6×1010kg=6×107t；

（2）∵P=UI，

当用200千伏的高压输送电能时，电路中的电流：

I1=

P 
U1
=
6×105×103W
200×103V
=3000A，

这条输电线损耗的电功率：

P1=I12R=（3000A）2×20Ω=1.8×108W=180000kW，

当改用1000千伏的特高压输电时，电路中的电流：

I2=

P 
U2
=
6×105×103W
1000×103V
=600A，

这条输电线损耗的电功率：

P2=I22R=（600A）2×20Ω=7.2×106W=7200kW，

这条导线上损耗的电功率会减少：

△P=P1-P2=180000kW-7200kW=172800kW．

答：（1）一年至少要消耗6×107t煤炭；

（2）用200千伏的高压输送电能的功率为6×105千瓦，这条输电线损耗的电功率是180000kW，改用1000千伏的特高压输电，那么这条导线上损耗的电功率会减少172800kW．

问答题

The American economic system is organized around a basically private-enterprise, market-oriented economy in which consumers largely determine what shall be produced by spending their money in the marketplace for those goods and services that they want most. Private businessmen, striving to make profits, produce these goods and services in competition with other businessmen; and the profit motive, operating under competitive pressures, largely determines how these goods and services are produced. (47)Thus, in the American economic system it is the demand of individual consumers, coupled with the desire of businessmen to maximize profits and the desire of individuals to maximize their incomes that together determine what shall be produced and how resources are used to produce it.
(48)An important factor in a market-oriented economy is the mechanism by which consumer demands can be expressed and responded to by producers. In the American economy, this mechanism is provided by a price system, a process in which prices rise and fall in response to relative demands of consumers and supplies offered by seller-producers. If the product is in short supply relative to the demand, the price will be bid up and some consumers will be eliminated from the market. (49)If, on the other hand, producing more of a commodity results in reducing its cost, this will tend to increase the supply offered by seller-producers, which in turn will lower the price and permit more consumers to buy the product. Thus, price is the regulating mechanism in the American economic system.
The important factor in a private-enterprise economy is that individuals are allowed to own productive resources (private property), and they are permitted to hire labor, gain control over natural resources, and produce goods and services for sale at a profit. (50)In the American economy, the concept of private property embraces not only the ownership of productive resources but also certain rights, including the right to determine the price of a product or to make a free contract with another private individual.
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单项选择题

()是以国债期货交易合约为标的，买卖双方通过交易所，约定在未来特定的交易日以约定的价格和数量进行券款交收的交易方式，是一种国债的衍生交易形式。

A．国债现券交易

B．国债回购交易

C．国债期货交易

D．国债继期交易
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