题目

听材料，回答问题。 （1） What is the probable relationship between the two speakers? A . Friends. B . Brother and sister. C . Husband and wife. （2） What is wrong with the woman's father? A . He has a bad cold. B . He is in hospital. C . He is seriously ill. （3） What did the doctor advise the woman's father to do? A . Go to work as well. B . Give up smoking. C . Stay at home for two weeks.在真空中，半径为r=3×10-2 m的圆形区域内有匀强磁场，方向如图3-2-2所示，磁感应强度B=0.2 T，一个带正电的粒子，以初速度v0=106 m/s从磁场边界上直径ab的一端a射入磁场，已知该粒子的比荷=108 C/kg，不计粒子重力，则： 图3-2-2（1）粒子在磁场中做匀速圆周运动的半径是多少？（2）若要使粒子飞离磁场时有最大偏转角，求入射时v0方向与ab的夹角θ及粒子的最大偏转角α.