A Velocity Selector Uses a Fixed Electric Field of Magnitude

Multiple Choice

A velocity selector uses a fixed electric field of magnitude E and the magnetic field is varied to select particles of various energies. If a magnetic field of magnitude B is used to select a particle of a certain energy and mass, what magnitude of magnetic field is needed to select a particle of equal mass but twice the energy?

A) 0.50 B
B) 1.4 B
C) 2.0 B
D) 0.71 B
E) 1.7 B