题目

如图所示，水平导线通以向右的恒定电流，导线正下方运动的电子（重力不计）的初速度方向与电流方向相同，则电子在刚开始的一段时间内做（ ）A.匀速直线运动 B.匀速圆周运动C.曲线运动，轨道半径逐渐减小 D.曲线运动，轨道半径逐渐增大 答案：【答案】D【解析】水平导线中通有稳定电流，根据安培定则判断导线下方的磁场方向垂直直面向里，且磁感应强度随着到导线距离的变大而逐渐变弱，由左手定则判断电子所受的洛伦兹力向下，其速率不变，而离导线越远，磁场越弱，磁感应强度越小，根据洛伦兹力提供向心力解得，可知电子的的轨迹根据句子意思，用括号中所给单词的适当形式填空，并将答案填写在相应位置上。【1】In class, we often have a __________ (discuss) to express our own thoughts.【2】Unbelievable! Jack even fell __________ (sleep) when Jay Zhou appeared on stage.【3】Compared with 4G networks, 5G networks will allow people to download date even__________ (quick).【4】Though Jessica is an exchange student, she is used to __________ (chat) with others in Chinese.【5】Avengers: Endgame described as the best film of the series __________ (win) a big success in April in China.