[填空题]
A doubly charged helium atom bah un8fs;:d4n hk)pc(su(c4 whosqi njr coij(s3u3490h e mass is $6.6 \times10^{-27 }\;kg$ is accelerated by a voltage of 2100 V.
(a) What will be its radius of curvature if it moves in a plane perpendicular to a uniform 0.340-T field? m
(b) What is its period of revolution? $ \times10^{ -7}\;s$
