Hai điện tích q1 = -10-6C, q2 = 10-6C đặt tại hai điểm A, B cách nhau 40cm trong chân không. Cường độ điện trường tại điểm M cách A 20cm và cách B 60cm có độ lớn là
A. E =
B. E =2.105V/m
C. E =
D. E =
Đáp án và lời giải
Đáp án:B
Lời giải:
E =2.105V/m
Điểm M nằm ngoài AB và phía A. Cường độ điện trường do q1 và q2 gây tạiM là ngược chiều ta có:
Bạn có muốn?
Xem thêm các đề thi trắc nghiệm khác
Xem thêm
Chia sẻ
Một số câu hỏi khác có thể bạn quan tâm.
-
Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions:
Humans have struggled against weeds since the beginnings of agriculture. Marring our gardens is one of the milder effects of weeds - any plants that thrive where they are unwanted. They clog waterways, destroy wildlife habitats, and impede farming. Their spread eliminates grazing areas and accounts for one-third of all crop loss. They compete for sunlight, nutrients, and water with useful plants. The global need for weed control had been answered mainly by the chemical industry. Its herbicides are effective and sometimes necessary, but some pose serious problems, particularly if misused. Toxic compounds threaten animal and public health when they accumulate in food plants, groundwater, and drinking water. They also harm workers who apply them. In recent years, the chemical industry has introduced several herbicides that are more ecologically sound. Yet new chemicals alone cannot solve the world’s weed problems. Hence, scientists are exploring the innate weed-killing powers of living organisms, primarily insects and microorganisms. The biological agents now in use are environmentally benign and are harmless to humans. They can be chosen for their ability to attack selected targets and leave crops and other plants untouched. In contrast, some of the most effective chemicals kill virtually all the plants they come in contact with, sparing only those that are naturally resistant or have been genetically modified for resistance. Furthermore, a number of biological agents can be administered only once, after which no added applications are needed. Chemicals typically must be used several times per growing season.
Question: Which of the following terms does the author define in the first paragraph?
-
Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions:
Humans have struggled against weeds since the beginnings of agriculture. Marring our gardens is one of the milder effects of weeds - any plants that thrive where they are unwanted. They clog waterways, destroy wildlife habitats, and impede farming. Their spread eliminates grazing areas and accounts for one-third of all crop loss. They compete for sunlight, nutrients, and water with useful plants. The global need for weed control had been answered mainly by the chemical industry. Its herbicides are effective and sometimes necessary, but some pose serious problems, particularly if misused. Toxic compounds threaten animal and public health when they accumulate in food plants, groundwater, and drinking water. They also harm workers who apply them. In recent years, the chemical industry has introduced several herbicides that are more ecologically sound. Yet new chemicals alone cannot solve the world’s weed problems. Hence, scientists are exploring the innate weed-killing powers of living organisms, primarily insects and microorganisms. The biological agents now in use are environmentally benign and are harmless to humans. They can be chosen for their ability to attack selected targets and leave crops and other plants untouched. In contrast, some of the most effective chemicals kill virtually all the plants they come in contact with, sparing only those that are naturally resistant or have been genetically modified for resistance. Furthermore, a number of biological agents can be administered only once, after which no added applications are needed. Chemicals typically must be used several times per growing season.
Question: Which of the following statements about the use of chemical agents as herbicides would the author most likely agree?
-
Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions:
Humans have struggled against weeds since the beginnings of agriculture. Marring our gardens is one of the milder effects of weeds - any plants that thrive where they are unwanted. They clog waterways, destroy wildlife habitats, and impede farming. Their spread eliminates grazing areas and accounts for one-third of all crop loss. They compete for sunlight, nutrients, and water with useful plants. The global need for weed control had been answered mainly by the chemical industry. Its herbicides are effective and sometimes necessary, but some pose serious problems, particularly if misused. Toxic compounds threaten animal and public health when they accumulate in food plants, groundwater, and drinking water. They also harm workers who apply them. In recent years, the chemical industry has introduced several herbicides that are more ecologically sound. Yet new chemicals alone cannot solve the world’s weed problems. Hence, scientists are exploring the innate weed-killing powers of living organisms, primarily insects and microorganisms. The biological agents now in use are environmentally benign and are harmless to humans. They can be chosen for their ability to attack selected targets and leave crops and other plants untouched. In contrast, some of the most effective chemicals kill virtually all the plants they come in contact with, sparing only those that are naturally resistant or have been genetically modified for resistance. Furthermore, a number of biological agents can be administered only once, after which no added applications are needed. Chemicals typically must be used several times per growing season.
Question: Which of the following best describes the organization of the passage?
-
Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions:
Let children learn to judge their own work. A child learning to talk does not learn by being corrected all the time. If corrected too much, he will stop talking. He notices a thousand times a day the difference between the language he uses and the language those around him use. Bit by bit, he makes the necessary changes to make his language like other people’s. In the same way, children learn all the other things they learn to do without being taught - to talk, run, climb, whistle, ride a bicycle - compare their own performances with those of more skilled people, and slowly make the needed changes. But in school we never give a child a chance to find out his mistakes for himself, let alone correct them. We do it all for him. We act as if we thought that he would never notice a mistake unless it was pointed out to him, or correct it unless he was made to. Soon he becomes dependent on the teacher. Let him do it himself. Let him work out, with the help of other children if he wants it, what this word says, what the answer is to that problem, whether this is a good way of saying or doing this or not. If it is a matter of right answers, as it may be in mathematics or science, give him the answer book. Let him correct his own papers. Why should we teachers waste time on such routine work? Our job should be to help the child when he tells us that he can’t find the way to get the right answer. Let’s end all this nonsense of grades, exams, and marks. Let us throw them all out, and let the children learn what all educated persons must someday learn, how to measure their own understanding, how to know what they know or do not know. Let them get on with this job in the way that seems most sensible to them, with our help as school teachers if they ask for it. The idea that there is a body of knowledge to be learnt at school and used for the rest of one’s life is nonsense in a world as complicated and rapidly changing as ours. Anxious parents and teachers say, “But suppose they fail to learn something essential, something they will need to get on in the world?” Don’t worry! If it is essential, they will go out into the world and learn it.
Question: What does the author think is the best way for children to learn things?
-
Read the following passage and mark the letter A, B, C,or D on your answer sheet to indicate the correct answer to each of the questions:
The Nobel prizes, awarded annually for distinguished work in chemistry, physic, physiology or medicine, literature, and international peace, were made available by a fund bequeathed for that purpose by Swedish philanthropist, Alfred Bernard Nobel. The prizes, awarded since 1901, are administered by the Nobel Foundation in Stockholm. In 1969, a prize for economics endowed by the Central Bank of Sweden was added. Candidates for the prizes must be nominated in writing by a qualified authority in the field of competition. Candidates are judged by Swedish and Norwegian academies and institutes on the basis of their contribution to mankind. The awards are usually presented in Stockholm ion December 10, with the King of Sweden officiating, an appropriate tribute to Alfred Nobel on the anniversary of his death. Each prize includes a gold medal, a diploma, and a cash award of about one million dollars.
Question: How often are the Nobel prizes awarded?
-
Read the following passage and mark the letter A, B, C,or D on your answer sheet to indicate the correct answer to each of the questions:
The Nobel prizes, awarded annually for distinguished work in chemistry, physic, physiology or medicine, literature, and international peace, were made available by a fund bequeathed for that purpose by Swedish philanthropist, Alfred Bernard Nobel. The prizes, awarded since 1901, are administered by the Nobel Foundation in Stockholm. In 1969, a prize for economics endowed by the Central Bank of Sweden was added. Candidates for the prizes must be nominated in writing by a qualified authority in the field of competition. Candidates are judged by Swedish and Norwegian academies and institutes on the basis of their contribution to mankind. The awards are usually presented in Stockholm ion December 10, with the King of Sweden officiating, an appropriate tribute to Alfred Nobel on the anniversary of his death. Each prize includes a gold medal, a diploma, and a cash award of about one million dollars.
Question: What does this passage mainly discussed?
-
Read the following passage and mark the letter A, B, C,or D on your answer sheet to indicate the correct answer to each of the questions:
The goal of Internet-based encyclopedia Wikipedia [www.wikipedia.org] is to give everyone on the planet access to information. Like other encyclopedias, Wikipedia contains lots of information: more than 2.5 million articles in 200 different languages covering just about every subject. Unlike other encyclopedias, however, Wikepedia is not written by experts, but by ordinary people. These writers are not paid and their names are not published. They contribute to Wikipedia simply because they want to share their knowledge. Encyclopedias began in ancient times as collections of writings about all aspects of human knowledge. The word itself comes from ancient Greek, and means “a complete general education”. Real popularity for encyclopedias came in the nineteenth century in Europe and the United States, with the publication of encyclopedias written for ordinary readers. With the invention of the CD-ROM, the same amount of information could be put on a few computer discs. Then with the Internet, it became possible to create an online encyclopedia that could be constantly updated, like Microsoft’s Encarta. However, even Internet-based encyclopedias like Encarta were written by paid experts. At first, Wikipedia, the brainchild of Jimmy Wales, a businessman in Chicago, was not so different from these. In 2001, he had the idea for an Internet-based encyclopedia that would provide information quickly and easily to everyone. Furthermore, that information would be available free, unlike other Internet encyclopedias at that time. But Wales, like everyone else, believed that people with special knowledge were needed to write the articles, and so he began by hiring experts. He soon changed his approach, however, as it took them a long time to finish their work. He decided to open up the encyclopedia in a radical new way, so that everyone would have access not only to the information, but also to the process of putting this information online. To do this, he used what is known as “Wiki” software [from the Hawaiian word for “fast”], which allows users to create or alter content on web page. The system is very simple: When you open the web site, you can simply search for information or you can log on to become a writer or editor of articles. If you find an article that interests you – about your hometown, for example – you can correct it or expand it. This process goes on until no one is interested in making any more changes.
Question: Wikipedia is written by_________.
-
Read the following passage and mark the letter A, B, C,or D on your answer sheet to indicate the correct answer to each of the questions:
The Nobel prizes, awarded annually for distinguished work in chemistry, physic, physiology or medicine, literature, and international peace, were made available by a fund bequeathed for that purpose by Swedish philanthropist, Alfred Bernard Nobel. The prizes, awarded since 1901, are administered by the Nobel Foundation in Stockholm. In 1969, a prize for economics endowed by the Central Bank of Sweden was added. Candidates for the prizes must be nominated in writing by a qualified authority in the field of competition. Candidates are judged by Swedish and Norwegian academies and institutes on the basis of their contribution to mankind. The awards are usually presented in Stockholm ion December 10, with the King of Sweden officiating, an appropriate tribute to Alfred Nobel on the anniversary of his death. Each prize includes a gold medal, a diploma, and a cash award of about one million dollars.
Question: A Nobel prize would NOT be given to _______.
-
Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35:
Many people today would like the traditional two-parent family back, that is to say, they want a man and a woman to [31]______ for life; they also think the man should support the family and the woman should stay home with the children. However, few families now [32]______ into this category. In fact, if more women decide to have children on their own, the single-parent household may become more typical than the traditional family in many countries. Also, unmarried couples may decide to have more children – or they might take in foster children or [33]______. And because people are staying single and living longer [often as widows], there may be more one-person households. [34]______ the other hand, some people believe similar events happen again and again in history: if this is true, people may go back to the traditional [35]_____ or nuclear family of the past. Others think the only certainty in history is change: in other words, the structure of the future family could begin to change faster and faster and in more and more ways.
Question 35:
-
Read the following passage and mark the letter A, B, C,or D on your answer sheet to indicate the correct answer to each of the questions:
The Nobel prizes, awarded annually for distinguished work in chemistry, physic, physiology or medicine, literature, and international peace, were made available by a fund bequeathed for that purpose by Swedish philanthropist, Alfred Bernard Nobel. The prizes, awarded since 1901, are administered by the Nobel Foundation in Stockholm. In 1969, a prize for economics endowed by the Central Bank of Sweden was added. Candidates for the prizes must be nominated in writing by a qualified authority in the field of competition. Candidates are judged by Swedish and Norwegian academies and institutes on the basis of their contribution to mankind. The awards are usually presented in Stockholm ion December 10, with the King of Sweden officiating, an appropriate tribute to Alfred Nobel on the anniversary of his death. Each prize includes a gold medal, a diploma, and a cash award of about one million dollars.
Question: Why were the prizes named for Alfred Nobel?