在真空室内速度为v=6.4×107m/s的电子束连续地沿两平行导体极板的中心线射

题型:计算题

问题:

在真空室内速度为v=6.4×107m/s的电子束连续地沿两平行导体极板的中心线射入,如图所示,极板长L=8.0×10-2m,两极板间距离d=5.0×10-3m,两极板不带电时,电子束将沿中心线射出极板。今在两极板间加上50Hz的交变电压U=U0sin100πtV,发现有时有电子从两极板之间射出,有时则无电子从两极板间射出,若有电子射出的时间间隔与无电子射出的时间间隔之比△t1:△t2=2:1,则所加的交变电压的最大值U0为多大?已知电子的质量为m=9.1×10-31kg,电量为e=1.6×10-19C。

考点:带电粒子在电场中的偏转
题型:计算题

I go to Australia for a meeting with my workmate, Chris. We decide(决定) to drive across the country after the meeting. The drive will take four days and most of it was across the desert(沙漠).

The first day is a lot of fun because we are happy to hear each other's jokes(玩笑). But on the third day, we begin to get bored. We are quite quiet for some hours when(这时) Chris sees some kangaroos(袋鼠).We are both excited and decide to take a closer(近一点的) look. Chris drives very quickly to catch up with(赶上)them. We got closer and closer. Suddenly(突然), we hear a loud BANG!

Chris stops the car and we get out. Beside the car is a large kangaroo(袋鼠) lying on the ground. Chris goes over to it and puts his cap on its head. He takes off his sunglasses and puts them on the kangaroo and does the same with his jacket. Then he puts his arm around the kangaroo and tells me to take a photo of them together. I take out my camera. When I am focusing(调整焦距)the camera, I sees the kangaroo move(移动). It suddenly wakes up, and runs away before we can do anything.

I start laughing(大笑) but Chris looks worried. He says his wallet is in the jacket. I start laughing even louder(更大). I stop laughing when he says that our car keys are also in the jacket.

小题1:Why does the writer go to Australia?

A.For a meeting.

B.For a trip.

C.For a holiday.

D.To see his friend.小题2:How long will the drive take according to their plan?

A.One day.

B.Four days.

C.Half a month.

D.Two months.小题3:What does the underlined word "bored" mean in Chinese?

A.无聊的

B.口渴的

C.饥饿的

D.困倦的小题4:Why do they hear a loud BANG?

A.Because there is something wrong with their car.

B.Because someone else is hunting(捕猎) kangaroos.

C.Because something falls off (从---掉下) their car.

D.Because their car knocks down(撞倒) a kangaroo.小题5:What can we know from the passage?

A.The writer takes a photo of Chris and the kangaroo.

B.The kangaroo runs away together with Chris’s wallet and their car keys in his jacket.

C.They decide to walk across the desert.

D.The writer is still(仍然)very happy at the end of the story.

题型:计算题

造成抽油机平衡重块固定螺栓松动故障的原因是()。

A、缺少锁紧螺母

B、抽油机负荷重

C、冲数过高

D、缺少润滑油

题型:计算题

GSM系统是()系统。

A.频分多址

B.时分多址

C.码分多址

题型:计算题

对新入网网元,综合网管采集上来后,无需建立完整的归属和关联关系,就能进行后续的相关应用和管理。

题型:计算题

恶性程度最高的乳癌类型是

A.髓样癌
B.炎性乳癌
C.湿疹样癌
D.浸润性小叶癌
E.浸润性导管癌

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