问题 选择题

下列关于电荷、电荷量的说法正确的是 (      )

A.自然界只存在三种电荷:正电荷、负电荷和元电荷

B.物体所带的电荷量可以是任意值

C.物体所带的电荷量只能是某些特定的值

D.物体的带电量可以是2×10-19C

答案

答案:C

题目分析:自然界中有两种电荷,将其中一种称为正电荷,另一种称为负电荷,元电荷是指最小的电荷量,元电荷又称“基本电量”,是电荷量的单位,而不是电荷,常用符号e表示,任何带电体所带电荷量都是e的整数倍,故A错误;物体带电是由于电荷的移动而导致,因此带电量均是元电荷的整数倍关系,所以电荷量只能取一些不连续的值,即只能是某特定的值,故B错误,C正确;物体的带电量都是1.6×10-19C的整数倍,故D错误.所以选C.

阅读理解

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A device that stops drivers from falling asleep at the wheel is about to undergo(接受) testing at Department of Transport laboratories and could go on sale within 12 months.

The system, called driver Alert, aims to reduce deadly road accidents by 20%--40% that are caused by tiredness. Airline pilots can also use it to reduce the 30% of all pilot-error accidents that are related to tiredness.

Driver Alert is based on a computerized wristband. The device, worn by drivers or pilots gives out a sound about every four minutes during a car journey. After each sound the driver must respond by pressing the steering wheel. A sensor in the wristband detects this pressing action and measures the time between the sound and the driver’s response.

Tiredness is directly related to a driver’s response time. Usually, a watchful driver would take about 400 milliseconds to respond, but once that falls to more than 500 milliseconds, it suggests that the driver is getting sleepy.

In such cases the device gives out more regular and louder sounds, showing that the driver should open a window or stop for a rest. If the driver’s response continues to slow down, the sounds become more frequent until a nonstop alarm warns that the driver must stop as soon as possible.

The device has been delivered to the department’s laboratories for testing. If these tests, scheduled for six months’ time, are successful, the makers will bring the product to market within about a year.

68. How should a driver respond to the sounds from Driver Alert?

A. By sounding a warning.   B. By touching the wristband.

C. By checking the driving time. D. By pressing the steering wheel.

69. We can learn from the text that the driver needs to stop for a break when his response time is ________

A. about 400 milliseconds    B. below 500 milliseconds

C. over 500 milliseconds      D. about 4 minutes

70. When the driver gets sleepy while driving, Driver Alert ______.

A. moves more regularly      B. stops working properly

C. opens the window for the driver      D. sounds more frequently and loudly

71. According to the text, Driver Alert ______.

A. aims to reduce tiredness-related accidents

B. has gone through testing at laboratories

C. aims to prevent drivers from sleeping

D. has been on sale for 12 months

多项选择题