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Một điện tích điểm q = -2.10-7C di chuyển được đoạn đường 5cm dọc theo một đường sức của điện trường đều có cường độ điện trường 5000V/m. Công của lực điện thực hiện trong quá trình di chuyển của điện tích q là – Học trắc nghiệm
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Question 47: 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: We live in a world of tired, sleep deprived people. In his book Counting Sheep, Paul Martin – a behavioral biologist – describes a society which is just too busy to sleep and which does not giveleeping the importance it deserves. Modern society has invented reasons not to sleep. We are now a 24/7 society where shops and services must be available all hours. We spend longer hours at work than we used to, and more time getting to work. Mobile phones and email allow us to stay in touch round the clock and late-night TV and the Internet tempt us away from our beds. When we need more time for work or pleasure, the easy solution is to sleep less. The average adult sleeps only 6.2 hours a night during the week, whereas research shows that most people need eight or even eight and a half hours’ sleep to feel at their best. Nowadays, many people have got used to sleeping less than they need and they live in an almost permanent state of ‘sleep debt’. Until the invention of the electric light in 1879 our daily cycle of sleep used to depend on the hours of daylight. People would get up with the sun and go to bed at nightfall. But nowadays our hours of sleep are mainly determined by our working hours (or our social life) and most people are woken up artificially by an alarm clock. During the day caffeine, the world’s most popular drug, helps to keep us awake. 75% of the world’s population habitually consume caffeine, whichup to a point masks the symptoms of sleep deprivation. What does a chronic lack of sleep do to us? As well as making us irritable and unhappy as humans, it also reduces our motivation and ability to work. This has serious implications for society in general. Doctors, for example, are often chronically sleep deprived, especially when they are on ‘night call’, and may get less than three hours’ sleep. Lack of sleep can seriously impair their mood, judgment, and ability to take decisions. Tired engineers, in the early hours of the morning, made a series of mistakes with catastrophicresults. On our roads and motorways lack of sleep kills thousands of people every year. Tests show that a tired driver can be just as dangerous as a drunken driver. However, driving when drunk is against the law but driving when exhausted isn’t. As Paul Martin says, it is very ironic that we admire people who function on very little sleep instead of criticizing them for being irresponsible. Our world would be a much safer, happier place if everyone, whatever their job, slept eight hours a night. All of the following are mentioned as those whose performance is affected by ‘sleep debt’ EXCEPT .