[填空题]
(a) What value of magnetic field would make+ e/nsvzz3j3 w(/s gb*;g7ge:ttxjdj a beam of b* lihvvmpb559zk ((qelectrons, traveling to the right at a l (vm(59 hzpb*qv5bikspeed of $4.8 \times10^{ 6}\;m/s$ go undeflected through a region where there is a uniform electric field of 10,000V/m pointing vertically up? $ \times10^{ -3}\;T$(retain one decimal places)
(b) What is the direction of the magnetic field if it is known to be perpendicular to the electric field?
(c) What is the frequency of the circular orbit of the electrons if the electric field is turned off? $ \times10^{7 }\;Hz$
