问题 选择题

关于闭合电路的性质,下列说法正确的是(     ) 

A.外电路断路时,路端电压最大

B.外电路短路时,电源功率最大

C.外电路电阻增大时,电源的输出功率变大

D.电动势越大,则非静电力在电源内部从负极向正极移送单位电荷量的电荷做功越多

答案

ABD

题目分析:A、外电路断路时,路端电压等于电源的电动势,路端电压最大;正确

B、外电路短路时,通过电源的电流最大,由可知,电源功率最大;正确

C、当内外电阻相等时电源的输出功率最大,则外电路电阻增大时,电源的输出功率不一定变大;错误

D、由电动势的定义知,电动势越大,则非静电力在电源内部从负极向正极移送单位电荷量的电荷做功越多;正确

故选ABD

点评:对于电源的两个特殊状态:短路和断路,路端电压和电流要通过欧姆定律在理解的基础上记忆.路端电压随外电阻的增大而增大,知道当时电源的输出功率最大。

阅读理解

阅读理解。

                                              The Cost of Higher Education

     Individuals (个人) should pay for their higher education.

    A university education is of huge and direct benefit to the individual. Graduates earn more than

nongraduates. Meanwhile, social mobility is ever more dependent on having a degree. However, only

some people have it. So the individual, not the taxpayers, should pay for it. There are pressing calls on

the resources (资源) of the government. Using taxpayers' money to help a small number of people to

earn high incomes in the future is not one of them.

    Full government funding (资助) is not very good for universities. Adam Smith worked in a Scottish

university whose teachers lived off student fees. He knew and looked down upon 18thcentury Oxford,

where the academics lived comfortably off the income received from the government. Guaranteed

salaries,  Smith argued, were the enemy of hard work;and when the academics were lazy and

incompetent, the students were similarly lazy.

    If students have to pay for their education, they not only work harder, but also demand more from their

teachers. And their teachers have to keep them satisfied. If that means taking teaching seriously, and

giving less time to their own research interests, that is surely something to celebrate.

    Many people believe that higher education should be free because it is good for the economy (经济).

Many graduates clearly do contribute to national wealth, but so do all the businesses that invest (投资)

and create jobs. If you believe that the government should pay for higher education because graduates

are economically productive, you should also believe that the government should pay part of business

costs. Anyone promising to create jobs should receive a gift of capital from the government to invest.

     Therefore, it is the individual, not the government, who should pay for their university education.

1.The underlined word "them" in Paragraph 2 refers to ________.

A. taxpayers      

B. pressing calls

C. college graduates  

D. government resources

2.The author thinks that with full government funding ________.

A. teaching are less satisfied

B. students are more demanding

C. students will become more competent

D. teachers will spend less time on teaching

3.The author mentions businesses in Paragraph 5 in order to ________.

A. argue against free university education

B. call on them to finance students' studies

C. encourage graduates to go into business

D. show their contribution to higher education

问答题 简答题