What is the velocity must a proton have if it is to go undeflected when passing through a magnetic field of
B= Tesla which is crossed with an electric field of E= V/m?
Here, the E-field is the red arrows, and the B-field is the blue crosses. So the E-field points down and the B-field points
into the screen. The proton is the black dot, moving with some speed v shown by the black arrow.