问题 实验题

某同学要测量一待测电阻Rx的阻值,备选器材如下:

电流表A,量程为50mA,内阻r=30Ω;   电压表V1,量程为3 V,内阻约为2 kΩ;

电压表V2,量程为15 V,内阻约为4.5kΩ;待测电阻Rx,阻值约为20Ω;

定值电阻R0,阻值为10.0Ω;            滑动变阻器R1。最大阻值为20Ω;

滑动变阻器R2,最大阻值为200Ω;      电源E,电动势为4V,内阻忽略不计;

开关S,导线若干.

实验中要求电表的读数超出量程的,能测多组数据,并有尽可能高的测量精确度.

(1)该实验中电压表应选用        ,滑动变阻器应选用         

(2)在下面的方框中画出实验电路图,标明仪器代号;

(3)如果在实验中,电压表的示数为U时,电流表的示数为I,则待测电阻Rx的阻值表达式为____________.

答案

(1)V1  R1   (2)如图  (3)

题目分析:(1)题中要求电表读数要超出量程的,故电压表选V1;经分析可知应选择滑动变阻器分压式接法,故选择R1,电流表内阻已知,当电压表和电流表同时接近满偏时,总电阻为60Ω,故电路如图所示;由欧姆定律知,待测电阻为

单项选择题

Actually, though, America, the "land of immigrants", has always had people of many different nationalities and languages. The 1990 census indicates that almost 14% of Americans speak a non English language at home. Yet only 3% reported that they spoke English "not well" or "not at all". That means that slightly more than one out of 10 Americans could be considered bilingual.
Besides that, many high school, college students, and even some elementary school students are required to take a foreign language as a part of their curriculum. In addition to old standbys like Spanish, German and French, more and more students are opting for Eastern European and Asian languages. Of course, not all students keep up their foreign language abilities. As the old saying goes, " If you don’t use it. " But still, a growing number of Americans are coming to appreciate the benefits of being multilingual.
Ethnic enclaves, found particularly in major metropolitan centers, have preserved the language and culture of American immigrants. Some local residents can function quite well in their native language, without having to bother learning English. Regions such as southern Florida and the Southwest have numerous Spanish speaking neighborhoods. In fact, Spanish speakers—numbering over 17 million—compose the largest non English linguistic group in America. But Chinese, Vietnamese, Italian, Polish and many other ethnic group add to the linguistic flavor of America. Foreign languages are so commonly used in some ethnic neighborhoods that visitors might think they are in another country!
Although some Americans welcome this linguistic and cultural diversity, others have begun to fear that the English language is being threatened. Since the 1980s, the "English Only" movement has sought to promote legislation which would establish English as the "official language" and restrict the use of non English language. However, some groups, including TESOL, the organization for Teachers of English to Speakers of Other Language, object to such "language restrictionism". Their view, known as "English Plus", suggests that Americans should have respect for people’s native language and help them fit into the mainstream of society. But so far, 19 states have passed English Only legislation, and the topic is the focus of an ongoing debate.
Whether or not English is the official language of the United States, it remains the "language of wider communication". Nearly everyone recognizes the need to develop proficiency in English in order to do well in America. To help those who want to brush up on their English skills, English as a Second Language (ESL) classes around. Cities with large numbers of recent immigrants often set up bilingual education programs to teach students content subjects in their native language while they improve their English. Language educators often have p and divergent views as to which approach helps learners achieve better results: a bilingual approach, an ESL approach or even a pure immersion ("sink or swim") approach. However, all these teachers share a common commitment: to help students function well in English.
Americans recognize that English is the international language, and people with good English skills can get by in many international settings. On the other hand, in a world growing increasingly smaller, second language skills can be a great favor. They can build cross cultural bridges and give people an edge in a variety of career field. Indeed, lack of foreign language proficiency can limit one’s chances for advancement and keep one in a cultural dead end street. As many people in America are discovering, being monolingual is no laughing matter.

The word "bilingual" (Line 5, Paragraph 1) means ______.

A.being able to speak two languages
B.being able to speak three languages
C.being able to speak four languages
D.being able to speak five languages

判断题