Physics crossed fields magnetic fields?

An electrons acceelrated from rest through potential differnce V1=1.00 kV enters the gap between two parallel plates having seprataion d=20 mm and the potential differnc V2=100V. The lower plate is taat the lower potetnial (neg sign). Neglect fringing and assume that the electron's velcoity vector is... show more An electrons acceelrated from rest through potential differnce V1=1.00 kV enters the gap between two parallel plates having seprataion d=20 mm and the potential differnc V2=100V. The lower plate is taat the lower potetnial (neg sign). Neglect fringing and assume that the electron's velcoity vector is prependiuclar to the E field vector betweeb the plates. In unit vector notation waht unifom magnetic field allows the electron to travel in a straight line through the gap?
I understand how tod o the question the E field is directed toward the bottom plate (neg) the electrostatic force Fe is upward since the electroin is moving toward the pos plate upward and the Fb has to be downward -j didrction to balance out the force.

HOW DO YOU FIND THE DIRECTION OF THE MAGNETIC FIELD B, WHY IS IT IN -K DIRECTION INTO THE PAPER?
I know that Fb=qv cross B well we want to find the diretion of the B not Fb, right? since we know Fb is in -j direction and v is in i diretion so I dont get it, how can you use right hand rule to find the direction of B? i though you use right hand rule to find direciton of Fb?


explain and shwo steps
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