一束带电粒子以同一速度vo并从同一位置进入匀强磁场，在磁场中它们的轨迹如图所示．若粒子A的轨迹半径为r 1，粒子B的轨迹半径为r 2，且r 2=2r 1，q1、q2分别是它们的带电量，m1、m2分别是它们的质量．则下列分析正确的是（ ）
A．A带负电、B带正电，荷质比之比为
：q1 m1
=1：1q2 m2
B．A带正电、B带负电，荷质比之比为
：q1 m1
=1：1q2 m2
C．A带正电、B带负电，荷质比之比为
：q1 m1
=2：1q2 m2
D．A带负电、B带正电，荷质比之比为q1 m1：
=1：2q2 m2 
A向左偏，B向右偏，根据左手定则知，A带正电，B带负电．根据半径公式r=
，知荷质比mv qB
=q m
，v与B不变，所以荷质比之比等于半径之反比，所以v Br
：q1 m1
=2：1．故C正确，A、B、D错误．q2 m2
故选C．
阅读下列材料, 从所给的五个选项(A、B、C、D、E)中，选出符合各小题要求的最佳选项，其中有一项是多余选项。 53. ___________ Rik has graduated from ahigh school and he wants to find a job with high pay in the town. He has just passed his driving test. He loves vehicles a lot. 54. ___________ Mrs. Sphinx is a middle aged woman. She is out of work now. It is hard for her to find a suitable job for the lack of special train when young. However, she has a large family with four children to support. 55. ___________ Christina, young and attractive, is good at English. She wants to go abroad to run a hotel after graduation. But she is lack of experience. So she needs practice. 56. ___________ Jacky is a newly-graduated college student. He majors in computer. He also plays guitar fairly well. So he entertains himself with it when he is free.
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