题目

示波管中有两个偏转电极，其中一个电极 XX′上可以接入仪器自身产生的锯齿形电压，叫扫描电压。如图甲所示， XX′极板长L＝0.2m，板间距d＝0.2m，在金属板右 端竖直边界MN的右侧有一区域足够大的匀强磁场，磁感应强度B＝5×10－3T，方向垂 直纸面向里。现将 X′板接地，X极板上电势φ随时间变化的规律如图乙所示。有带正电的q粒子流以速度 v0＝1×105m/s，沿水平中线 OO′连续射入电场中，粒子的比荷为＝1×108 C/kg，重力忽略不计，在每个粒子通过电场听下面一段对话，回答第1-3题。1. How many subjects did the woman learn in middle school?A. Four.  B. Five.  C. Six.2. What do we know about the woman from the conversation?A. She didn’t do well in Biology.B. She did very well in History.C. She is good at playing football.3. What’s the probable relationship between the speakers?A. Coach and player.       B. Teacher and student.C. Old classmates.