如图(甲)所示，两水平放置的平行金属板C、D相距很近，上面分别开_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题问答题

如图(甲)所示，两水平放置的平行金属板C、D相距很近，上面分别开有小孔O和，水平放置的平行金属导轨P、Q与金属板C、D接触良好，且导轨在磁感应强度为B₁＝10T的匀强磁场中，导轨间距L＝0.50m．金属棒AB紧贴着导轨沿平行导轨方向在磁场中做往复运动．其速度图像如图(乙)，若规定向右运动速度方向为正方向，从t＝0时刻开始，由C板小孔O处连续不断飘入质量为m＝3.2×10^－21kg、电量q＝1.6×10^－19C的带正电的粒子(设飘入速度很小，可视为零)．在D板外侧有以MN为边界的匀强磁场B₂＝10T，MN与D相距d＝10cm，B₁和B₂方向如图(甲)所示(粒子重力及其相互作用不计)，求：

(1)0～4.0s时间内哪些时刻发射的粒子能穿过电场并飞出磁场边界MN？

(2)粒子从边界MN射出来的位置之间最大的距离为多少？

答案

（1）　0.25s＜t＜1.75s．

（2）7.3cm．

(1)只有当CD下正上负使其间电场向上，即AB棒向右运动时，粒子才可能从O运动到，而粒子要飞出磁场边界MN的最小速度v₀必须满足

d＝，

　设CD间电压为U，则qU＝，

　由①②解得U＝25V．

　AB棒切割磁感线产生电动势为E，则

　 U＝E＝B₁Lv，解得v＝5m/s．

　所以根据图(乙)可以推断得出：

　0.25s＜t＜1.75s．

　(2)当AB棒速度最大，即＝20m/s时，产生感应电动势为，可得

＝B₁L＝100V．

　此时带电粒子经加速后速度为v，根据动能定理，有

　 q＝mv²，

　解得 v＝100m/s．

　此时带电粒子的轨道半径为

＝＝0.2m．

　出射点与的水平距离为

x＝－＝0.027m＝2.7cm．

　粒子从边界MN射出来的位置间最大距离为

　 s＝d－x＝7.3cm．

材料分析题

以下是记者对两个村书记的采访记录：

对比甲村和乙村，结合经济常识，说明在社会主义新农村建设中如何通过“强化产业支撑”增加农民收入。

________________________________________________________________________________________________________________________________________________________________________________________

完形填空

Travis laughed as he tore at the wrapping paper on his birthday present. He was so       ! Finally, he would have the coolest pair of name-brand basketball shoes.
All the guys on his team were wearing the name-brand shoes of a popular basketball       , Chuck Hart.         Hart was criticized for his poor sportsmanship and infamous      , he was a great player. In fact, Travis wasn't thinking about Hart' s behavior; he had only expected to see Hart’s       on the side of the box. The first indication that something was       came as he tore away the last piece of paper. Not Hart’s. The new shoes were the name-brand of another player, Robert Ryann, who was       for his amazing work in the community.
Travis’s hands       ; his heart stopped. It wasn't that the Ryann shoes weren’t nice, but what would his friends think ?
They were the wrong shoes and Travis would be       by the other players. When he looked up into his dad' s eyes, however, Travis decided he      not tell him. "'Thanks, Dad. I was really hoping for shoes," Travis said as he pulled the shoes out of the box.
Next morning his dad drove him to school. When they       in front of his destination, Travis slowly opened the car door. Just then, his dad stopped him.
“Hey, Travis, wait a minute, look…” his dad said       ,“Travis, I know those aren’t the shoes you had hoped for, but I saw the names of the two guys and made a（n）      . The guy whose name is on those shoes,” he said, pointing down at Travis’s feet, “is someone I       . Do you know how often Ryann has found himself in      ?”
“No,” Travis said.
“Never. He’s never talked back to his coach or started a fight, and he’s a team player. You could have acted like a (n)       when you didn’t get the shoes you wanted, Travis,       you were polite and made the best of it. You have such a good       , like the guy whose name is on these shoes. I’m hoping that someday, your name will be on the coolest pair of shoes I’ll ever see.”
When Travis looked down at his feet, he saw the shoes       . His dad had used his mind and heart to give the son a thoughtful       .

B．performance

C．delightedly

D．differently