an electron accelerated from rest through potential difference V1=0.868 kV enters the gap between two parallel plates having separation d = 21.9 mm and potential difference V2= 91.2 V. The lower plate is at the lower potential. Neglect fringing and assume that the electron's velocity vector is perpendicular to the electric field vector between the plates. In unit-vector notation, what uniform magnetic field allows the electron to travel in a straight line in the gap?
KE = QV
KE = 1/2 mv^2
FE = QE
FB = Qv X B
The Attempt at a Solution
i know that Q and m are the charge an mass of an electron
to calculate E, i used V2, 91.2V.
I use the equations to solve for v
i know that for the electron to go straight through, the FE=FB,
so i got E = vB
then i solved for B
and since B is a cross product of vectors on an xy plane, It HAS to only have a direction perpendicular to them on the z axis
it asks for the answer in vector notation so
in the end, i get 0i + 0j + 2.38e-4k T
but it's wrong...
I have a feeling that this is supposed to be one of the easier questions too :S