试题与答案

如图,直角坐标系在一真空区域里,y轴的左方有一匀强电场,场强方向跟y轴负方向成θ

题型:计算题

题目:

如图,直角坐标系在一真空区域里,y轴的左方有一匀强电场,场强方向跟y轴负方向成θ=30°角,y轴右方有一垂直于坐标系平面的匀强磁场,在x轴上的A点有一质子发射器,它向x轴的正方向发射速度大小为v=2.0×106m/s的质子,质子经磁场在y轴的P点射出磁场,射出方向恰垂直于电场的方向,质子在电场中经过一段时间,运动到x轴的Q点。已知A点与原点O的距离为10cm,Q点与原点O的距离为(20-10)cm,质子的比荷为。求:

(1)磁感应强度的大小和方向;

(2)质子在磁场中运动的时间;

(3)电场强度的大小。

答案:

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In the US and Britain, the slogan around colleges was “Save water. Shower with a friend.” Now, Wuhan University has come up with another system for the campus bathhouse. It charges students for the amount of time in a shower. Before entering the bathhouse, students pay for the amount of time they want in the shower with cash or their student ID card. The clock starts ticking the minute the tape is turned on. It pauses when a button is pressed for soap. An integrated circuit(IC) card reader at each tap shows the time. No money, no water. The benefits of the new system can be seen with the old system, which charged 1 yuan for each person regardless of time in the shower. The university used about 320 tones of water daily under the old system, but only 160 tons now.

Many students use the new system but opinions on it are divided. Some students say it is bad because bathing had become a sort of race. Many people using it for the first time are not sure how long they need to shower. Some might be embarrassed if their time is up and they’re still covered in soap. They have to ask the bathhouse worker to help them buy extra time.

“It’s a flaw in the system that you can not buy extra time on the ID card,” said Ren, a freshman in Wuhan University. The university is also considering some students’ suggestions that they be allowed to pay after they’ve finished the shower. Not surprisingly, some are complaining about losing the hour shower. But many students say the move helps them develop a water-saving sense.

Without the time limits, most students tended to shower for 30 to an hour in the bathhouse.

Some even used the hot water to wash their clothes. “In my experience, 10-20 minutes is enough,” said Dai Zhihua, a third-year student who usually takes 8 minutes.

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C. If money runs out, there will be no water.

D. Having finished bathing, the student has to pay for it.

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B. The new operation can raise students’ environmental awareness.

C. a similar operation has been set in other universities.

D. The university has saved a lot of water by using the new system.

55. In which column can you find this passage?

A. People.    B. Society.  C. Campus Life.   D. Lifesty

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