2022 英语周报 七年级 新课程 44答案

第一节【参考范文】Dear annieIm Li Hua. Hows everything going these days? I'd like to ask you to write an article for our schools English newspaperThe"Culture field "section is very popular among us students. And here are some relevant details about the articles we areeager for. Would you please write something about how Americans spend their holidays and festivals, which is interesting andinformative? 400 words would be fine. Could we have your article before June 10?I'm looking forward to your replySincerely yoursLi Hua

14【解析】(1)粒子在磁场中做匀速圆周运动,运动轨迹如图所示,设轨迹半径为n∷∷∷∷:x∴:x氵∴:只∷D·22由洛伦兹力充当向心力可知qB=m,解得n=(2分)粒子在國外正方形磁场中的轨迹半径也为n=R粒子恰好不射出正方形区域,则正方形的边长L=2r1+2r=4R(2分(2)粒子在國形磁场中做圆周运动的周期T:=3,在圆形磁扬中运动时间4=2(2分粒子在國形以外的区域做圆周运动的周期T=2,在圆形以外的磁场中运动时间2=≥T2=3TR(2分)则再次回到M点的时间t=41+h=E(2分)

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