一束质量为m、电量为q的带电粒子以平行于两极板的速度v0进入匀强_爱下问搜题

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问题填空题

一束质量为m、电量为q的带电粒子以平行于两极板的速度v₀进入匀强电场，如图所示，如果两极板间电压为U，两极板间的距离为d，板长为L，设粒子束不会击中极板，则粒子从进入电场到飞出极板时电势能的变化量为______（粒子的重力忽略不计）

答案

粒子在电场中做类平抛运动，根据牛顿第二定律与运动学公式可得，经过电场后的偏转位移y=

1

2

at2=

1

2

qU

md

(

L

v0

)2

而电场中，电势能的变化量等于电场力做功的多少，即△E=W=qEy=q

U

d

y

由以上两式，综合而得，飞出极板时电势能的变化量为

q2U2L2

2md2

v

20

故答案为：

q2U2L2

2md2

v

20

听力题

小题1:Few students ______( ask ) to work hard at their lessons here, are they?

小题2:The police promised that they ______(solve) the case as soon as possible.

小题3:The school trip we look forward to ______(take) place this Saturday.

小题4:My parents didn’t go to the cinema with me, they ______ already______(fly) to America.

小题5:______(catch) up with his friends, he ran as fast as he could.

小题6:China ______(send) up several spacecraft into space in the last few years.

小题7:The charity show ______(organize) by my classmates last year was a great success.

小题8:I’m sorry I didn’t catch what you said because I ______ (type) the letter.

问答题简答题

卫星广播电视节目非恶意干扰的几种情况。