问题 问答题

如图所示,A、C、D为三个平行板电容器,MN为中心轴,D1D2与MN的距离相等,O为电容器C的中点,整个装置处于真空中.A1A2足够大且足够近,距离为d0=1mm,中间有磁感应强度B=9×10-2T的匀强磁场.A1与D1相连,A2与D2相连并接地,C1C2加上电压U0=90V,侧面有小孔S1和S2,D1D2的极板长均为L=10cm.今在O点源源不断的加入初速度为零的中性粒子,粒子在O点处被特殊装置剥离成2价正离子和电子,而不改变速度大小.已知电子质量为m=9×10-31kg,该2价正离子的质量是电子质量的2×104倍,电子电量为e=1.6×10-19C,.(忽略粒子重力)

(1)求电子通过孔S2的速度大小.

(2)若整个装置达到稳定状态后,电子刚好能从D中飞出,求D1D2两板间的距离为多少?

答案

(1)电子在电场中加速,由动能定理得:

1
2
eU0=
1
2
m
v21

求得,电子速度:v1=

eU0
m
=4×106m/s

(2)2价正离子通过S1时,有:

1
2
(2e)U0=
1
2
m′
v22

得:

v2
=
2eU0
m′
=
1
100
eU0
m
=4×104m/s

2价正离子在磁场中偏转,半径为 r=

m′v2
2eB
=2.5×10-2m>
d0
2

使得AD带正电,AD带电稳定时,有:2ev2B=2e

U
d0

则得 U=Bv2d0=3.6V

电子进入D1D2间做类平抛运动,当电子刚好能从D中飞出时,有:

d
2
=
1
2
at2

a=

eU
md

t=

L
v1

联立解得:d=

L
v1
eU
m
=0.02m=2cm

答:

(1)电子通过孔S2的速度大小是4×104m/s.

(2)若整个装置达到稳定状态后,电子刚好能从D中飞出,D1D2两板间的距离为2cm.

阅读理解

阅读理解。

    Playworld is a large theme park just outside New York. We employ hundreds of people and are still

growing. We provide entertainment of many kinds: shows, parades, rollercoasters, carrousels, and of

course our latest addition: The Landslider. Our guests can stay in the Playworld Hotel and dine in one

of our fine restaurants.

    If you are looking for a growing fun, and innovative environment, consider joining the Playworld

Community.

    At present, we are looking for Waiters / Actors.

    Your main task will be serving food in the Western Grill in the evenings. During 3 afternoons per week

you will also play a minor part in the play: Let's Go West.

    Qualifications: Education at college level is required. Some work experience in a restaurant is preferred.

Acting experience would be an advantage, a working knowledge of German and French is desirable. Spanish

is a plus. We can offer you the opportunity to develop a personal career plus an attractive salary and extra

benefit package.

     Playworld is an equal opportunity employer.

     If you want to join our team, send your letter of application and resume:

     PLAYWORLD

     P.O Box 6514

     New York, NY 76156

1. " Playworld" is a place mainly for ______. [ ]

A. watching plays

B. enjoying food

C. having fun

D. training actors

2. "Carousel" is most probably a kind of ______. [     ]

A. sport

B. entertainment

C. food

D. park

3. If you get the job, you will ______. [ ]

A. play the hero in the play "Let's Go West"

B. work 3 afternoons per week

C. have to study Spanish

D. be free in the mornings

4. Which of the following applicants is likely to be accepted? [ ]

A. Name                              Liu Gang

     Sex                                Male

     Age                                26

     Education                       College 

     Work Experience             No

     Foreign Languages           French

B. Name                               Mary Smith

    Sex                                  Female

    Age                                  18 

    Education                          Middle School 

    Work Experience               3 weeks in restaurants

     Foreign Languages            French & Spanish

C. Name                               Jim White

     Sex                                  Male

     Age                                  23

     Education                         High School

     Work Experience               3 years as an active member of the school troupe (剧团) 

     Foreign Languages             French

D. Name                                Hillary Bush

     Sex                                   Female 

     Age                                   17

     Education                           High School

     Work Experience                2 weeks as a waitress in a restaurant: performed in 3 plays 

      Foreign Languages             German, French & Spanish

单项选择题 A1/A2型题